1. 1. Intracellular concentrations of putrescine, spermidine and spermine in Leishmania donovani were measured in (a) freshly isolated amastigotes, (b) cells permitted to transform for 6 hr and (c) transformed promastigotes. 2. 2. All three polyamines were found in freshly isolated amastigotes but spermine was not detected in promastigotes. 3. 3. Cells permitted to transform for 6 hr showed a drop in their spermine concentration although no visible cytodifferentiation had occurred by this time. 4. 4. Conversion of [14C]ornithine to spermine was found in both amastigotes and 6 hr transformed cells but not in promastigotes; control preparations from uninfected spleen converted very small amounts of [14C]ornithine to spermine. 5. 5. Putrescine levels in promastigotes increased more than 17-fold over that found in amastigotes. 6. 6. Ornithine decarboxylase activity was found in all stages. 7. 7. This is the first report of the presence of spermine in a hemoflagellate. © 1980.