A decision of special interest to the biotechnology community, Hitzeman v Rutter, 58 USPQ 2d 1161 (Fed Cir 2001), was delivered by the United States Court of Appeals for the Federal Circuit (CAFC or Federal Circuit) on March 21. The case arose as an appeal from the US Patent and Trademark Office (PTO) Board of Appeals and Interferences and it involved a determination of who is entitled to receive a US patent covering the particulate hepatitis B surface antigen produced in yeast cells, which is an effective human vaccine against hepatitis B. Prior to this invention, it was doubted by informed scientists that satisfactory hepatitis B surface antigen for vaccine purposes could be achieved using recombinant yeast cells as host cells, since bacterial host cells transformed with DNA encoding the hepatitis B surface antigen had been shown to produce a non-particulate antigen having no capability to impart immunity to hepatitis B in humans.