Much progress has been made since the concepts of bioavailability and bioequivalence were first defined; advances in pharmacokinetics, biopharmaceutics, and drug analysis have all made an impact. However,‘there are some unresolved problems that require urgent attention, if only to assure the credibility of the bioavailability and bioequivalence testing processes’, said Professor Gerhard Levy from the Department of Pharmaceutics, State University of New York, Buffalo, US, at the British Pharmaceutical Conference [Warwick, UK; September 1995]. Professor Levy discussed bioavailability and bioequivalence testing from the US perspective during a session entitled, ‘Bioequivalence and Generic Prescribing’ at the meeting.