Recently, it has been shown that interleukin-7 (IL-7) is able to induce secretion of cytokines and tumoricidal activity by human monocytes. This study shows that treatment of murine macrophages infected with Leishmania major with IL-7 without any other stimulus reduced the percentage of infected cells, as well as the parasite burden per cell, in a dose-dependent manner to a limited degree (45% reduction of the number of amastigotes per 100 macrophages). Simultaneous treatment of macrophages with gamma interferon and IL-7 led to nearly complete (> 99%) elimination of amastigotes. Addition of anti-tumor necrosis factor alpha or N omega-monomethyl-L-arginine acetate reversed the leishmanicidal effects of IL-7, and production of nitric oxide was induced in the presence of IL-7.