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Trichomonas vaginalis grown for 16 h in the presence of [14C]spermine formed a high intracellular pool of [14C]spermidine and a small but detectable pool of [14C]putrescine. When [3H]putrescine was added to the growth medium, a large intracellular pool of [3H]putrescine was found, but it was not further metabolized, confirming previous studies suggesting the absence of a forward-directed polyamine synthetic pathway in T. vaginalis. Spermidine:spermine N1-acetyltransferase (SSAT) and polyamine oxidase enzyme activities were detected which collectively converted spermine to spermidine. Polyamine oxidase was localized in the hydrogenosome-enriched fraction, whereas SSAT was found predominantly in the cytosolic fraction. In the presence of saturating substrate, the trichomonad SSAT had an activity of 0<39O0<09 nmol minN1 (mg protein)N1 (the mean of five analyses) and an apparent Km for spermine of 1<7 lM. The enzyme was competitively inhibited by di(ethyl)norspermine with a Ki of 28 lM. Growth studies indicated that 50 lM di(ethyl)norspermine caused a 68 % and 84 % reduction in the intracellular concentrations of spermidine and spermine, respectively. The trichomonad polyamine oxidase required FAD as a cofactor and had an apparent Km of 6<0 lM forN1-acetylspermine. The potential of bis(alkyl) polyamine analogues as antitrichomonad agents is discussed