The clinical behaviour and post-operative course of 60 patients who had undergone obstetrics or gynaecological surgery is compared. In 30 cases (20 obstetric and 10 gynaecological), antibiotic prophylaxis took the form of a single i.m. injection of 600 mg of lincomycin and 80 mg of gentamycin, 30 minutes before the operation. In the remaining 30 cases (20 obstetric, 10 gynacological), the antibiotic cover was administered postoperatively by i.v. injection of doxicyclin (100 mg every 12 hours for 3 days and 100 mg every 12 hours per os for a further 2 days). From a comparison of the 2 groups, and keeping obstetric and gynaecological cases separate, it is concluded that preoperative antibiotic prophylaxis is comparable in its results to post-operative antibiotic cover. Postoperative haematochemical tests were also done and, as has been reported, showed no significant alterations from the tests administered preoperatively, thus confirming the high tolerance of the drugs in question in the above-stated doses. No cochleovestibular disturbances were encountered nor were drug-resistant bacteriological strains. The efficacy of this prophylactic treatment is confirmed and though comparable in results to the alternative postoperative types is indubitably advantageous both in the lower cost to the community and the short duration of the treatment itself.