An estimated 2-3 billion people in the less developed countries suffer from infections, often multiple, caused by a variety of parasitic organisms. These infections are frequently debilitat­ ing rather than fatal, and the toll in human misery is fearsome. To this may be added the prevalence of similar diseases in do­ mestic animals, which diminish supplies of animal pro tein. As the world population increases, the already enormous problem also continues to grow. The resources of the less developed nations are inadequate for solving the problem, and in the developed countries a lack of interest in tropical diseases has meant low priority for research. Two recent methodological advances now raise the real possibility of a systematic and effec­ tive attack upon these diseases - hybridoma and recombinant nucleic acid technologies. The combination of these with the still necessary clinical, parasitological and imrnunological information permits a logical, planned and realistic approach to diagnosis and treatment. The central aim of these modem techniques is to define antigens with regard to diagnosis, protection and pathology. In the case of some diseases, work has already commenced along these lines; in the case of others, knowledge lags a long way behind. This volume represents a summary of current knowledge about a wide, representative spectrum of tropical diseases. There is considerable common ground between the different infections as regards objectives and the methods for achieving them.