Caprine Trypanosoma (N.) congolense infections were treated with sinefungin, an antifungal antibiotic nucleoside. Single doses from 10 to 20 mg/kg bodyweight given intramuscularly were not curative for goats; single doses of 25 and 50 mg/kg were toxic, and caused death. Five and 7.5 mg/kg administered twice daily over a three-day period, resulted in a cure in 2 animals, while 2 others relapsed. All animals relapsed when given a single daily dose of 5 or 7.5 mg/kg for 4 consecutive days. When such doses were given twice a day, they caused death in 50% of the goats and the remainder were cured. Raised serum urea levels indicated the severe nephrotoxic side-effects of sinefungin even at subcurative levels. Histopathological examinations revealed an acute tubulonephrosis.