Can an abandoned application be used as prior art?

Yes, an abandoned application can be used as prior art, but the extent of its use depends on several factors. Under MPEP 2127, abandoned applications that have been published can be used as prior art as of their publication date for all they teach. Unpublished abandoned applications may be available as prior art under certain circumstances, such as when they are incorporated by reference in a U.S. patent. It’s important to note that the abandonment status itself does not negate the application’s potential as prior art. For specific rules on using abandoned applications as prior art, consult MPEP 2127 and MPEP 901 on prior art.