A comparison has been made of the efficiency of a 2-day course of metronidazole (Flagyl) with that of a similar course of nimorazole (Naxogin) in the treatment of trichomoniasis. Of the 105 consecutive patients treated, 72 were finally included in the study (38 on metronidazole and 34 on nimorazole). Follow-up tests indicated an overall cure rate of 84-3 per cent. in those given Flagyl and 85-3 per cent. in those given Naxogin. Consorts were treated in just over 55 per cent. of cases in both groups. An attempt has been made to classify the recurrences as either 'primary' treatment failures or re-infections. Although both drugs were effective in the majority of cases, 'primary' treatment failure appeared to be commoner in the group receiving metronidazole. It is emphasized that the total dose of metronidazole was substantially lower than that recommended by the manufacturers.