The role of the essential nutrients, vitamins A, B (complex), C and E and iron, as prophylactic as well as supportive therapy in experimental visceral leishmaniasis (VL), was studied in hamsters. Prophylactic administration of vitamin C (50, 100 and 250 mg/kg) from day 15 to day 0 (15 doses) significantly reduced the intake of Leishmania donovani in hamsters but had no therapeutic effect. In contrast, vitamins A, B complex and E and iron, whether used prophylactically or therapeutically, promoted parasite multiplication. The efficacy of sodium stibogluconate, a reference antileishmanial drug, was appreciably improved in animals administered prophylactically with vitamin C. However, supplementation of vitamin C during established infections resulted in reduced drug action. The results show that the prophylactic use of vitamin C may prevent the onset of leishmania infection and cautions against the indiscriminate use of nutrient supplements such as vitamin A, B complex, and E and iron in VL endemic areas.