37 CFR 1.121 is the USPTO regulation that sets out how you amend a pending patent application. It governs changes to the three parts of the application that get amended during examination: the claims, the specification, and the drawings. Each part has its own formatting rules, and the rules are strict. A non-compliant amendment is not quietly overlooked. The USPTO issues a Notice of Non-Compliant Amendment and you have to fix and resubmit, often against a running response deadline.
One limit sits above all the formatting mechanics: you cannot introduce new matter. Federal patent law prohibits adding technical content, structural features, or functional descriptions that were not in the original specification, claims, or drawings as filed.1GovInfo. 35 USC 132 – Notice of Rejection; Reexamination This applies to claim language, specification edits, and drawing changes alike.
Amending the Claims
Any amendment that changes, cancels, or adds a claim must include a complete listing of every claim ever presented in the application, including canceled and withdrawn ones, in ascending numerical order. The claim listing has to start on its own sheet, and no sheet with claim text can contain any other part of the amendment.2eCFR. 37 CFR 1.121 – Manner of Making Amendments in Applications
Status Identifiers
Every claim in the listing carries a parenthetical status identifier immediately after its number. The regulation recognizes seven:
- (Original): a claim as originally filed that has never been amended
- (Currently amended): a claim being changed in this amendment
- (Previously presented): a claim amended in an earlier filing but not being changed now
- (New): a claim being added for the first time
- (Canceled): a claim that has been removed
- (Withdrawn): a claim removed from examination, often after a restriction requirement
- (Not entered): a claim the USPTO declined to enter
If a withdrawn claim is being amended, combine the identifiers as “(Withdrawn — Currently amended).”
Showing the Changes
A claim marked “(Currently amended)” must be presented in full with markings against the most recent prior version. Added text is underlined. Deleted text carries a strike-through. For deletions of five or fewer consecutive characters, you may use double brackets instead, and if strike-through is hard to read on the deleted text, double brackets are required.
Claims with any other status identifier appear without markings. Canceled claims show only the claim number and “(Canceled)” with no text. Original and previously presented claims appear in their current clean form, so the examiner ends up with a complete, readable set alongside the marked-up changes.
Amending the Specification
Specification changes work by replacement, not description. You do not tell the examiner in a cover letter what you want changed. You supply the actual replacement text with markings.
Replacing or Adding Paragraphs
To edit text within the specification, submit replacement paragraphs or replacement sections showing the full text with all changes marked. Added text is underlined; deleted text gets strike-through; double brackets are available for deletions of five characters or fewer.2eCFR. 37 CFR 1.121 – Manner of Making Amendments in Applications An entirely new paragraph must be underlined in full so the examiner can see that every word is new.
Deleting Whole Paragraphs
Deleting an entire paragraph works differently, and this is where people get tripped up. You provide an instruction that clearly identifies the paragraph to be removed, either by paragraph number or by quoting enough of the beginning and end to make identification unambiguous. You do not submit the deleted paragraph’s text with strike-through or double brackets. The instruction alone is enough.3United States Patent and Trademark Office. MPEP 714 – Amendments, Applicant’s Action
Substitute Specification
When the marked-up specification becomes too hard to follow, you can file a substitute specification that replaces all the descriptive text (everything except the claims). A substitute specification requires a marked-up copy showing every change from the prior version, a clean copy without markings, and a statement that no new matter has been introduced.4eCFR. 37 CFR 1.125 – Substitute Specification You can file one at any point before you pay the issue fee, and the USPTO can order one if the file has become difficult to read. Partial paragraph amendments, unlike a substitute specification, do not get a clean copy. The marked-up version is the only submission.
Amending the Drawings
Drawings follow their own rules under 37 CFR 1.121(d). You cannot mark up or alter the originally filed drawing sheets. Any change, however small, requires a new replacement sheet.
The replacement sheet is labeled “Replacement Sheet” in the top margin and must include every figure that appeared on the prior version of that sheet, including figures you did not change. A sheet holding an entirely new figure is labeled “New Sheet” instead. All replacement drawings must comply with USPTO drawing standards under 37 CFR 1.84.5eCFR. 37 CFR 1.121 – Manner of Making Amendments in Applications
Your amendment paper must include a detailed explanation of every change to the drawings, either in a dedicated drawing amendment section or in the remarks. You may include an annotated copy of the amended figure labeled “Annotated Sheet” in the margin. That annotated sheet is optional unless the examiner asks for one, in which case it becomes mandatory. Drawings are subject to the same new matter bar as everything else: you can correct errors, clarify existing features, or bring drawings into line with an amended specification, but you cannot add structure that was not part of the original disclosure.
When You Can File
The rules shift depending on where your application sits in examination.
Preliminary Amendments
A preliminary amendment reaches the USPTO on or before the mailing date of the first Office action. If you file it within three months of the application’s filing date (or three months from national stage entry for international applications), it will not be disapproved, and those periods cannot be extended.6eCFR. 37 CFR 1.115 – Preliminary Amendments After that window, the USPTO may disapprove a preliminary amendment that would unduly interfere with preparation of the first Office action. A preliminary amendment that cancels every claim without presenting any new or substitute claims will always be rejected.
Timing also affects new matter analysis: a preliminary amendment filed on the same day as the application becomes part of the original disclosure; one filed after the filing date does not.
After Final Rejection
Once the examiner issues a final rejection, your options narrow. You can cancel claims, fix formatting issues the examiner identified earlier, or rewrite rejected claims to present them more clearly for appeal. Anything beyond that requires a showing of good and sufficient reasons for why the amendment is needed and why it was not filed earlier.7eCFR. 37 CFR 1.116 – Amendments and Affidavits or Other Evidence After Final Action and Prior to Appeal
Filing an after-final amendment does not stop the clock. Whether the examiner admits or refuses it, your response deadline keeps running from the mailing date of the final Office action. Miss that deadline and the application goes abandoned no matter what amendment is pending.
Excess Claim Fees
Amendments that add claims can trigger excess claim fees. The standard filing fee covers up to three independent claims and twenty total claims. Each independent claim beyond three costs $600 at the standard rate ($240 small entity, $120 micro entity). Each claim beyond twenty total costs $200 ($80 small entity, $40 micro entity).8United States Patent and Trademark Office. USPTO Fee Schedule These fees apply whether the excess claims appeared in the original filing or arrive later by amendment, and they are due when you file the amendment that pushes the count over either threshold. Going from three independent claims to six adds $1,800 at the standard rate.
What Happens If the Amendment Is Non-Compliant
If your amendment fails the formatting requirements, the USPTO sends a Notice of Non-Compliant Amendment identifying what failed and what is needed to fix it. What that notice means for your deadline depends on which amendment tripped it.
- Preliminary amendment filed after the filing date: two months to fix, no extensions. Miss the deadline and the USPTO examines the application as if the preliminary amendment does not exist.
- Preliminary amendment filed on the filing date: two months, extensions available. Failure to respond results in abandonment of the entire application.
- Amendment responding to a non-final Office action, including RCE submissions: two months, extensions available. Failure to respond results in abandonment.
- After-final amendment: the examiner attaches the non-compliance notice to an advisory action, and no new period is set. Your clock is still running from the final Office action, and you must respond to the final action to avoid abandonment.
The abandonment risk is easy to underestimate.3United States Patent and Trademark Office. MPEP 714 – Amendments, Applicant’s Action A formatting slip in an otherwise strong amendment can kill an application if the applicant does not treat the notice with the same urgency as an Office action.
What 37 CFR 1.121 Does Not Cover
Reissue applications follow a different amendment procedure under 37 CFR 1.173, not the rules described here.2eCFR. 37 CFR 1.121 – Manner of Making Amendments in Applications And once a patent issues, 37 CFR 1.121 no longer applies at all. Minor clerical or typographical mistakes in an issued patent are handled through a certificate of correction under 35 U.S.C. 255; substantive errors require a reissue application.9United States Patent and Trademark Office. MPEP 1481 – Certificates of Correction – Applicant’s Mistake