The aim of this study was to assess the influence of iv tramadol on opioid requirement in the early postoperative period. The subjects were 90 patients scheduled for colon surgery (hemicolectomy) who received general anesthesia using the (N2O/O2) isoflurane technique. Thirty patients (group I) were administered 100 mg of tramadol iv before induction of general anesthesia (preemptive analgesia). Group II (30 patients) was administered 100 mg of tramadol iv immediately after peritoneal closure (preventive analgesia) and control group (30 patients) received 100 mg of tramadol iv immediately after operation. Following the operation, all patients were administered tramadol in the PCA-iv mode in order to treat postoperative pain. In the postoperative period, the following parameters were measured: pain intensity (using VAS), total consumption of tramadol, time until the first PCA activation, and frequency of side effects (drowsiness, nausea, vomiting). In patients of groups I and II who had received preemptive or preventive analgesia, a significantly lower total consumption of tramadol, as compared with control group, was observed in the early postoperative period. However, the time until the first PCA activation was significantly shorter in group I as compared to the other two groups. No significant differences between the groups were found regarding pain intensity and frequency of side effects.