Despite the development of the most recent and powerful antimicrobic agents, surgical infections are to this day a constant threat to surgeons, rendering negative otherwise successful surgical results. It seems therefore essential that during surgical operations--which according to Altemeier's classification are defined as "contaminated" and "potentially contaminated"--patients undergo a perioperative antibiotic prophylaxis in order to assure elevated tissue levels of antibiotic as necessary. A perspective trial of two standard protocols of short term prophylaxis versus cefoperazone has been here outlined, given that in a recent study cefoperazone showed a positive effect in destroying the intestinal flora of patients even though this was carried out in experimental and not in clinical conditions. 177 patients were selected for this study with a breakdown of 26 and 42, that is twenty-six underwent potentially contaminated procedures and 42 contaminated procedures. Selecting at random, fifty percent of the first group was treated with cefoxitin, and the other half with cefoperazone; as far as the second group is concerned half the sample of patients was treated with cefoperazone and then compared with the other half who had been given an association of piperacillin and metronidazole. Primary septic complications amounted to 7.3% (13 cases); 7.6% in the first group (2 cases) and 21% in the second (9 cases). The different of sepsis between the two groups was not statistically significant although cefoperazone showed a higher septic result in contaminated surgery.(ABSTRACT TRUNCATED AT 250 WORDS)