The pathways of short-term tryptophan metabolism in rats infected with Trypanosoma brucei gambiense were studied to determine whether this amino acid undergoes rapid conversion to tryptophol and indole lactic acid, two metabolites produced in vitro by T. brucei gambiense. Intravenously administered L-[3-14C]-tryptophan was metabolized to at least two compounds in infected rats: tryptophol (indole ethanol) and indole acetic acid. Indole lactic acid was not detected as a metabolite. Approximately 76% of the labeled substrate was metabolized along these pathways in 30 min. Control rats exhibited no detectable metabolism of tryptophan during the same period. These results indicate that dietary tryptophan may be diverted from the kynurenine and serotonin pathways by parasite metabolism to compounds possessing potential pharmacological or toxic activity.