This study examines patients undergoing colorectal surgery for carcinoma, bacteriological data in faecal and systemic immunological data; these patients before surgery received short-term chemoprophylaxis with ceftriaxone (2 g e.v.) and thymopentina (1 phial/day for 15 days) and after surgery thymopentina (1 phial for three time a week). With these data the authors try to create immunomodulation and antibiotic chemoprophylaxis protocol for the reduction of the septic complications due to intestinal bacterial flora and immunological defence reduction.