The aim of the present report was to establish the effectiveness of different prophylactic antibiotic regimens and administration times in colorectal cancer surgery. Six thousand and sixty nine patients from 36 selected randomized clinical trials, published between 1980 and 1989, were reviewed. The occurrence of septic events, isolated bacterial strains, fever and postoperative hospitalization times were also analyzed. The therapeutic schedules that included the perioperative administration of antibiotics provided better results that those that did not (p. less than .0001 for infections both specifically related and unrelated to colorectal surgery). The number of postoperative administrations did not affect the clinical results, even if the predominant choice was to give more than one administration of antibiotics. A factorial design demonstrated that prolonging the perioperative administrations up to the postoperative period provided statistically significant benefits (p less than .0001) only with regard to the risk of infections that were not specifically related to colorectal surgery.