Purpuromycin and its semi-synthetic derivative MDL 63,604 had in-vitro activity similar to that of amphotericin B against isolates of Candida albicans. MDL 63,604 had activity similar to that of metronidazole against Trichomonas vaginalis. Both compounds were very active against most species of Gram-positive and Gram-negative anaerobes and against Gardnerella vaginalis. MDL 63,604 had significantly lower MICs than purpuromycin against T. vaginalis and most of the bacteria, probably due to antagonism of purpuromycin's activity by medium supplements (blood or serum). Purpuromycin or related compounds may have a potential role in the topical treatment of vaginitis and vaginosis.