The effect of preoperative unspecific immunomodulation with Propionibacterium granulosum KP-45 (P.g.) on postoperative complications and patient survival was evaluated in a prospectively randomized trial in patients with colorectal tumor resection. Patients of the therapy group (n = 51) received at least 3 days before operation an infusion of 10 mg P.g., patients of the control group (n = 49) were not treated at all. The wound infection rate and the number of re-explorations were significantly lower in the therapy group, however, patient survival and tumor recurrence rates were not positively affected by this P.g. pre-treatment.