Preemptive analgesia aims to prevent the sensitization of central nervous system, hence the development of pathologic pain after tissular injury. The aim of the study was to assess the effect of preincisional clonidine treatment on analgesic consumption and hemodynamic stability compared to clonidine administered at the end of the operation and control group. Ninety-one patients undergoing elective colorectal surgery were randomly assigned to four groups: peroral clonidine before operation, epidural clonidine before operation, epidural clonidine at the end of operation, and epidural saline before operation as a control group. After the operation, patient-controlled analgesia with epidural morphine was instituted. Analgesic consumption, blood pressure and heart rate were obtained at 1, 2, 6 and 24 h postoperatively, and the cumulative consumption of analgesics was assessed at the end of the study period. Significant differences (p < 0.05) in postoperative systolic blood pressure, with highest hemodynamic stability was observed at 1 h and 6 h in the group of patients administered epidural clonidine before operation. In this group of patients we found significant reduction in analgesic consumption during the study period (p < 0.05), compared to other groups. The cumulative consumption of analgesics assessed at the end of the study period was significantly reduced (p < 0.05) in the group of patients administered epidural clonidine before operation (8.40 +/- 3.74, respectively) as compared with the peroral clonidine before operation (16.79 +/- 5.75, respectively), epidural clonidine at the end of the operation (11.11 +/- 4.24, respectively) and control group of patients (18.00 +/- 6.45, respectively). Preincisional administration of epidural clonidine was associated with a significantly lower analgesic use, lower cumulative analgesic consumption and greater hemodynamic stability, in comparison with other groups.