Previous articles in this volume have considered the whole question of parasite vaccines from the immunological point of view. A backcloth of general concepts (Roitt, 1989) and strategies in the viral area (Schild, 1989) precedes consideration of problems specific to parasite vaccines (Mitchell, G. F. 1989). This leads on to reviews of progress to date in the development of vaccines for leishmaniasis (Modabber, 1989), malaria (Mitchell, G. H. 1989) and schistosomiasis (Sher, 1989) and in the development and use of veterinary vaccines (Morrison, 1989). I have been asked in this final chapter to take one step back from all of this and provide the alternative, chemotherapeutic, perspective. The reasons for the request are particularly pertinent, though rarely stated: antiparasite drugs already exist; if parasite vaccines are in fact developed, the way these drugs are used and the whole question of whether or not new ones are required, will have to be reconsidered. It is also a timely one: it is clear that the whole concept of a series of vaccines for the control of parasitic diseases has been so well sold, some would say oversold, that it is impacting on the resolve within the pharmaceutical industry to undertake new chemotherapeutic developments, at a time when this is already under severe strain because of financial considerations (Gutteridge, 1987 a). Hence my title: Parasite vaccines versus anti-parasite drugs: rivals or running mates?. I will try to answer it by, in turn, addressing three key questions. Why are we attempting to develop parasite vaccines? Will we be successful? If we are, will there still be a need for chemotherapy?