Abstract Antrycide and ethidium bromide — 2 cationic trypanocides — inhibited NAD-linked α-glycerophosphate dehydrogenase from Leptomonas sp. The kinetics of enzyme inhibition was determined by Lineweaver-Burk, Dixon, or direct linear plots. Inhibition by Antrycide was noncompetitive for dihydroxyacetone phosphate in the presence of saturating Mg 2+ or spermidine. With dihydroxyacetone phosphate at saturation, Antrycide inhibition was also noncompetitive with respect to Mg 2+ (K i = 115 μM) and spermidine (K i = 85 μM). Inhibition by ethidium in the presence of saturating dihydroxyacetone phosphate, was noncompetitive for Mg 2+ (K i = 400 μM) but mixed for spermidine (K i = 495 μM); inhibition was noncompetitive for dihydroxyacetone phosphate in the presence of saturating Mg 2+ or spermidine. Rabbit-muscle α-glycerophosphate dehydrogenase was inhibited at all concentrations of Antrycide and ethidium tested, but the Leptomonas enzyme was stimulated up to 3.5-fold by low concentrations of inhibitors in the absence of polyamine. New chemotherapeutic possibilities may thus be opened and an evolutionary distinction between trypanosomatid and mammalian enzyme.