Exposure of peripheral blood mononuclear cells to promastigotes of Leishmania aethiopica derived from patients with the self-limiting, localized form of the disease (local cutaneous leishmaniasis; LCL) preferentially induced mRNA for interferon (IFN)-gamma but little for interleukin (IL)-10. In contrast, stimulation of the same cells with promastigotes derived from patients with the persistent, disseminated form of the disease (diffuse cutaneous leishmaniasis; DCL) stimulated the expression of IL-10 rather than IFN-gamma. In general, parasites derived from LCL patients induced more expression of other cytokines tested, including IL-4, IL-6, and transforming growth factor-beta, although tumor necrosis factor-alpha was equivalent in cultures stimulated with LCL or DCL promastigotes. The results suggest that the antigen-specific immunosuppression observed in DCL patients and the resulting clinical picture could in part be due to the properties of the infecting parasite to induce more IL-10 than IFN-gamma.