The cytotoxicity of prodigiosin, an antibiotic and potential trypanocide produced by Serratia marcescens, and Benznidazole, a trypanocidal drug, were assayed on V79 fibroblast cell line. Three independent endpoints for cytotoxicity were evaluated; namely, the nucleic acid content (NAC), MTT reduction and neutral red uptake (NRU). IC50 values of 1-20 mu M were obtained for prodigiosin in the NRU, MTT and NAC tests. Prodigiosin had greater trypanocidal activity (IC50=5 mu M) than Nifurtimox (IC50 = 150 mu M) a known trypanocide drug used in Chagas' disease therapy. Benznidazole was less toxic (IC50 = 2000 mu M) than prodigiosin (IC50 = 1-20 mu M) in V79 cells based on the MTT and NAC assays. Benznidazole stimulated the NRU until 2 mM. Indeed, the cell viability measured with the NRU was higher at all concentrations of benznidazole tested than that measured by MTT reduction and NAC assays. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.1163237242