The attempt to restrict as much as possible the use of the antibiotics in surgery is related with the recent introduction of short term antibiotic prophylaxis. In this study the possibility to select among patients undergoing contaminated procedures those who can benefit more from short term antibiotic prophylaxis was considered. With this aim the nutritional status of 302 patients according to three parameters: serum albumin, total iron binding capacity and weight loss, was assessed. Results obtained from short term antibiotic prophylaxis with clindamycin and gentamicin in 149 patients (53.6% malnourished) were compared with those obtained in 153 patients (49.6% malnourished) who were not treated peroperatively. Wound infection rate in patients who received antibiotic prophylaxis was 6% versus 15% in the group which did not receive antibiotics peroperatively (p less than 0.025). A significant reduction was observed in malnourished patients while in the well-nourished the decrease was not significant. Malnourished patients seem to gain a specific benefit from antibiotic prophylaxis.