Can a best mode defect be cured by a later amendment?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

No, a best mode defect cannot be cured by a later amendment to the patent application. The MPEP 608.01(h) clearly states: If the best mode contemplated by the inventor at the time of filing the application is not disclosed, such defect cannot be cured by submitting an amendment seeking to put into the specification something required to be there when the application was originally filed.

This guidance is based on the case In re Hay, 534 F.2d 917, 189 USPQ 790 (CCPA 1976). The MPEP further advises: Any proposed amendment of this type should be treated as new matter. This means that the best mode must be disclosed at the time of filing, and attempts to add it later will be rejected as new matter.