There has been a rapid increase in the understanding of the mechanisms wherebyLeishmaniainfects mammalian hosts and evades the immune response. This, in turnm is driving the search for vaccines against leishmaniasis. Leishmaniasis is an infection in which the dichotomy between cellular (T-helper cell type 1) and humoral (T-helper cell type 2) responses is clearly characterized in murine models, but is unclear in humans. The diagnosis of infection may be improved by use of the polymerase chain reaction and by serology using a recombinant antigen, K39. The therapeutic choice in visceral leishmaniasis is aidedi by recent studies of the lipid-associated amphotericin B drugs and aminosidine (paramomycin). Unfortunately, inerferon-gamma, allopurinol, and topical aminosidine are all less effective treatments than was originally thought.