Ex Parte Reexamination: Requesting USPTO Review of a Patent

Ex parte reexamination is a formal USPTO administrative proceeding that allows any party — including the patent owner, a third party, or the USPTO itself — to request a second examination of an issued patent based on prior art in the form of patents or printed publications. Governed by 35 U.S.C. §§ 302–318 and implemented through 37 C.F.R. Part 1, Subpart D, the proceeding offers a mechanism for re-testing the validity of patent claims outside of litigation. It operates under a fundamentally different procedural structure than inter partes review or post-grant review, particularly in the degree of third-party participation permitted after filing.

Definition and scope

Ex parte reexamination is a patent office proceeding in which a requester presents prior art — specifically patents or printed publications — to the USPTO and asks whether that art raises a substantial new question of patentability (SNQ) with respect to one or more claims of an issued patent. The SNQ standard is the threshold gatekeeping requirement: the USPTO will not order reexamination unless the presented prior art raises a question of patentability that has not been previously considered by the Office, or was previously considered but not in the same light as now presented.

The proceeding is authorized under the America Invents Act (AIA), which preserved ex parte reexamination while simultaneously creating the Inter Partes Review and Post-Grant Review pathways. Understanding the regulatory context for patent law, including the statutory frameworks administered by the USPTO, is necessary to distinguish these overlapping validity-challenge mechanisms.

The scope of ex parte reexamination is bounded in two important ways:

1. Prior art type: Only patents and printed publications qualify as the basis for an SNQ. Physical evidence, on-sale bars, and prior public use cannot form the basis for reexamination under this proceeding.
2. Third-party participation: After the order for reexamination issues, a third-party requester loses the right to participate further. All subsequent prosecution occurs between the patent owner and the USPTO examiner — hence the term ex parte (one-sided).

How it works

The ex parte reexamination process follows a structured sequence defined by USPTO regulations at 37 C.F.R. §§ 1.510–1.570:

1. Filing the request: Any person — including the patent owner — may file a reexamination request. The request must identify each claim challenged, cite the prior art relied upon, and provide a detailed explanation of how that art raises an SNQ. As of the USPTO fee schedule effective January 2025, the filing fee for an ex parte reexamination request is $3,200 for a large entity (USPTO Fee Schedule).
2. Initial review: A USPTO examiner determines within three months whether the request raises an SNQ. If the SNQ threshold is not met, reexamination is denied and the requester receives a refund of a portion of the filing fee.
3. Order and examination: If the SNQ is found, the USPTO orders reexamination and assigns the case to a Central Reexamination Unit (CRU) examiner. The patent owner receives the first action on the merits.
4. Patent owner response: The patent owner may amend claims or submit arguments. New claims may be added, but no claim may be broadened during reexamination (35 U.S.C. § 305).
5. Prosecution and appeal: Prosecution continues until the examiner closes the record. If claims are finally rejected, the patent owner may appeal to the Patent Trial and Appeal Board and subsequently to the U.S. Court of Appeals for the Federal Circuit.
6. Certificate of reexamination: Upon conclusion, the USPTO issues a reexamination certificate canceling rejected claims, confirming patentable claims, or incorporating amended claims into the patent.

The entire proceeding is expected to conclude within 24 months of the order for reexamination under USPTO guidelines, though complex cases may extend beyond that target.

Common scenarios

Ex parte reexamination is most frequently initiated in four identifiable circumstances:

• Patent owner self-correction: A patent owner discovers prior art that potentially threatens claim validity and files a reexamination to proactively amend claims into a defensible form before litigation arises.
• Competitor invalidity challenges: A party facing an infringement allegation files a reexamination request to place adverse prior art on the record without becoming a party to a contested proceeding before the Patent Trial and Appeal Board.
• Pre-litigation risk assessment: A competitor conducting a freedom-to-operate analysis identifies a blocking patent and uses reexamination as a lower-cost alternative to litigation-based invalidity.
• Supplemental examination distinction: Unlike supplemental examination under 35 U.S.C. § 257, which is available only to patent owners and can address information beyond prior art, ex parte reexamination is open to third parties and limited strictly to patents and printed publications.

Decision boundaries

Choosing ex parte reexamination over other validity-challenge mechanisms requires mapping procedural trade-offs against strategic objectives.

Ex parte reexamination vs. Inter Partes Review (IPR): IPR, governed by 35 U.S.C. §§ 311–319, must be filed within one year of service of a complaint alleging infringement of the patent. Ex parte reexamination carries no such deadline. IPR allows full third-party participation throughout the proceeding; ex parte reexamination cuts off third-party participation after the request is filed. IPR applies an "unpatentability" standard under the preponderance of evidence threshold; ex parte reexamination proceeds through the ordinary examination framework.

Ex parte reexamination vs. Post-Grant Review (PGR): PGR must be filed within nine months of patent grant and permits challenges on any invalidity ground, not merely prior art patents and publications. Ex parte reexamination may be filed at any time during the life of the patent and is confined to the narrower prior-art-only basis.

The estoppel distinction: A third-party requester in ex parte reexamination incurs no statutory estoppel. By contrast, a petitioner who pursues IPR to a final written decision is estopped from raising in civil litigation or before the USPTO any ground that was raised or reasonably could have been raised during IPR (35 U.S.C. § 315(e)). This estoppel asymmetry is a central factor in the choice between proceedings.

Claim scope during reexamination: Because claims cannot be broadened during ex parte reexamination, the proceeding is unsuitable for a patent owner seeking to capture subject matter not covered by the original claims. The patent owner's amendments are restricted to narrowing the claims or adding dependent claims of narrower scope.

Practitioners and patent owners navigating these distinctions will find the overview of patent law topics a useful orientation to the full set of validity and enforcement mechanisms available under U.S. patent law.