Methylglyoxal is a toxic metabolite with growth inhibitory properties against Leishmania donovani promastigotes. We have shown in the present study that both log and stationary phase promastigotes of L. donovani can catabolize methylglyoxal to D-lactate as the major end product. The specific activity of methylglyoxal reductase was found to be the highest of all the catabolic enzymes. In contrast, the anabolic pathway for methylglyoxal could not be detected. Moreover, when control promastigotes or promastigotes in which the glycolytic pathway was inhibited were incubated with glucose, glycerol or dihydroxyacetone phosphate as energy source, neither methylglyoxal nor D-lactate could be detected.