Withdrawn patent data is now searchable on FreePatentsOnline. Withdrawn patents may be retrieved by searching the term "withdrawn" in the title field. This search retrieves approximately 22,600 withdrawn patents, the oldest being No. 4,246,372, withdrawn in 1981.
Allowed U.S. patent applications may be withdrawn prior to issue at the request of the applicant or USPTO provided certain conditions are met. Common reasons for withdrawal requests include the discovery of new prior art that could invalidate one or more claims in the allowed application, an error or illegality in the application, the applicant makes a request for continued examination (RCE) of an application or an interference. See Section 1308 of the Manual of Patent Examining Procedure for details.