Continued studies on pathogenesis and immunity are contemplated with Leishmania donovani in hamsters and mice. Both in vivo and in vitro studies are underway. "Toxic" products or exoantigens are being sought. Attempts continue to make use of a controlled culture system for infecting organisms to reduce variability in the model infections on which most conclusions on pathogenesis are based. The chick embryo has been infected with parasites via the intravascular route and gives hope of serving as a new model of infection, especially susceptible to environmental changes (temperature) while still representing an in vivo model.