Obtain a copy of the original patent application from the USPTO website or other online source. Check its issue date to find out if you are eligible to apply for re-examination of the patent; you may apply for reexamination within one year of the patent's issue date. If you are threatened with a patent infringement lawsuit with respect to the patent, however, you have four months from that time to apply for reexamination, even if the patent was issued more than one year ago.
Search for "prior art" — pre-existing technology that is identical or similar to the technology protected by the patent — by examining prior patent applications filed by others that may have features identical or similar to the patent you are challenging, and by referring to publications that may describe or refer to prior art that has not been patented. Online legal sources can help you perform a prior art search. Make copies of all publications upon which your research is based.
Prepare a patent reexamination statement. Your statement must explain why you believe the patent should not have been issued, identify the prior art that you believe invalidates the patent, specify which patent claims in the original patent application describe technology that is not unique, and explain exactly why the prior art you cite invalidates the patent claims you refer to. Most statements are lengthy and are prepared with the assistance of a patent lawyer.
Send a copy of your reexamination statement to the current patent holder by registered mail, return receipt requested. Keep the receipt as evidence that you notified the patent holder of your reexamination request.
Prepare a formal Request for Ex Parte Reexamination. The request must include the reexamination statement, a copy of the original patent application, a copy of all publications you relied on in your statement, and a certification that you served a copy of the reexamination statement on the current patent holder.
Mail your application package with the USPTO, along with a filing fee of several thousand dollars in certified funds, to: United States Patent and Trademark Office Customer Service Window, Mail Stop Ex Parte Reexam Randolph Building 401 Dulany Street Alexandria, VA 22314. The USPTO will decide within three months of your application filing date whether or not to order reexamination of the patent. If it orders re-examination, the patent holder will be notified and will be given an opportunity to respond within two months of the reexamination order.
Petition the USPTO director to reconsider the USPTO's denial of your reexamination request within one month, if the USPTO denies your reexamination request.
Submit a rebuttal to the patent holder's response within two months after the patent holder issues his response, if the USPTO decides to reexamine the patent and the patent holder submits a response. The USPTO will rule on the validity of the patent and will notify you of its decision.
Appeal the USPTO's decision to the U.S. Court of Appeals for the Federal Circuit in Washington, D.C. by filing a complaint within two months of the USPTO's decision, if you are dissatisfied with it. The court will arrange for your complaint to be served on the director of the USPTO.