This is an application for financial support for the 2nd International Workshop on is Pneumocystis carinii, Cryptosporidia and Microsporidum. This "experimentally difficult" group of opportunistic pathogens is responsible for much of the morbidity and mortality in AIDS. Despite the enormous medical and economic importance of these pathogens, there is relatively little research on their biology and modes of pathogenesis. There has been little improvement in therapy. To increase the quality and quantity of research on these pathogens it is necessary to bring together biologist with an interest in parasite biology with molecular biologists with an interest parasitology. We need to understand the clinical problems caused by these pathogens in the less developed countries and set up fruitful collaborations. These are the purposes of the workshop.