An open, randomised study was carried out to compare the efficacy and tolerability of pefloxacin plus metronidazole with gentamicin plus metronidazole in the coadjuvant treatment of generalised purulent peritonitis. The study was conducted on 100 patients of both sexes aged 18 to 93 years who had a diagnosis of diffuse purulent peritoneal infection. The antibiotics were administered up to a period of 4 days after all clinical or microbiological signs of infection had disappeared, with total treatment not exceeding 4 weeks. At the end of treatment, 6 of the 48 patients (12.5%) receiving pefloxacin plus metronidazole (PM group) and 21 of the 52 patients (40.4%) receiving gentamicin plus metronidazole (GM group) had localised infections. When the clinical efficacy of treatment was evaluated 15 days after discharge from the hospital, 39 patients in the PM group were found to be cured (81.2%), and there were 3 deaths (6.25%). In the GM group, 29 patients were found to be cured (55.7%), and there were 8 deaths (15.4%). Thus, the cure rate was significantly higher in the PM group than in the GM group (X2= 6.323; p < 0.05). We conclude that both antibiotic regimens utilised were effective as coadjuvants in the surgical treatment of diffuse purulent peritonitis, although the pefloxacin/metronidazole combination led to a better cure rate.