The influence of prophylactic tinidazole therapy on vaginal carriage rates of anaerobes and the development of post-operative anaerobic infection was studied in 100 women undergoing abdominal hysterectomy. Tinidazole prophylaxis (50 patients) led to a decrease of anaerobe vaginal carriage rate from 56% pre-operatively to 10 and 30% on the third and seventh post-operative days, respectively. In the control group (50 patients), no significant decrease in anaerobe yield was noted, corresponding percentages being 72, 64 and 74. Post-operative infection occurred in 34 cases (28 controls, 6 tinidazole prophylaxis). Wound swabs from patients in the latter group did not yield anaerobes on culture, and infections either resolved spontaneously (2 cases) or responded to tinidazole therapy, with or without addition of ampicillin and kanamycin (4 cases). In the control group, 21 cases of post-operative wound infection and 4 of vault infection were seen. Wound swabs from 6 of the former group yielded aerobes only and 10 mixed growth of aerobes/anaerobes. Post-operative wound/vault infections in control patients cleared spontaneously (18 cases) or responded to imidazole therapy, with or without ampicillin and kanamycin (7 cases). These data suggest that tinidazole may be a useful adjunct in imidazole prophylaxis and treatment of anaerobic infection.