Trichomonacidal treatment based on 5-nitroimidazoles is problematic both when Metronidazole, the drug of choice, is ineffective owing to the presence of resistant strains and when bacterial aerobic infections are present. Sulphimidazole (SIZ) possesses two distinct functional groups: one sulphonamide, the other 5-nitroimidazole. Since SIZ is active against aerobic and anaerobic bacteria, we set out to discover whether, in view of the presence of the 5-nitroimidazole group, it could also be effective against Trichomonas vaginalis. Twelve strains of T. vaginalis were cultured in Modified Thioglycate Medium in anaerobic conditions; subsequently, their growth was monitored in the presence of Metronidazole (MZ), SIZ, Sulphamethoxazole (SMX), Trimethoprim (TMP) and their associations. Eight strains proved to be sensitive to Metronidazole (minimum lethal concentration=0.5 microgml(-1)) and four to be resistant (minimum lethal concentration=40-60 microgml(-1)). SIZ was active against both the sensitive and the Metronidazole-resistant strains (minimum lethal concentrations=0.5-1 and 10 microgml(-1), respectively), thus showing that the chemotherapeutic activities of the two functional groups coexisting in SIZ remain unimpaired.