BACKGROUND Combined spinal-epidural (CSE) analgesia is becoming increasingly used to provide pain relief during labor. It combines both the rapid onset of the spinal analgesia and the flexibility of the epidural catheter. Intrathecal sufentanil provides rapid-onset and profound analgesia during the first stage of labor. The dose required to produce this effect can be associated with maternal respiratory depression, hypotension, nausea, or pruritus. The major concern of the anesthesiologist is to limit these side effects sources of discomfort to a parturient, by choosing the optimal dose of sufentanil or searching for an alternative. The purpose of this study is to compare tramadol and sufentanil used in CSE analgesia in terms of duration of analgesia and frequency of adverse maternal or fetal effects. METHODS Forty parturients requesting labor analgesia were included in this prospective study. In a combined spinal- epidural technique, at 3 to 4 cm cervical dilation, patients were randomly assigned to receive either one of the following intrathecal solutions: 2.5 mg sufentanil (n = 20) and 2.5 mg bupivacaine, or 25 mg tramadol (n = 20) and 2.5 mg bupivacaine. Visual analog scores for pain, blood pressure, heart rate, sensory levels, incidence of nausea and pruritus, motor blockade, and maternal satisfaction, were recorded. RESULTS Patients receiving 25 mg intrathecal tramadol with 2.5 mg bupivacaine had significantly longer-lasting analgesia (114 +/- 7 min). than those receiving 2.5 mg intrathecal sufentanil and 2.5 mg bupivacaine (54 +/- 11 min). No adverse maternal or fetal effects were noted in the group sufentanil. Five parturients of the tramadol group, presented vomiting 10 min after induction. There was no difference in the time from analgesia to delivery, incidence of operative or assisted delivery or cervical dilation. During labor, maternal satisfaction was good. CONCLUSIONS 2.5 micrograms of intrathecal sufentanil combined with 2.5 mg bupivacaine provides rapid-onset and profound analgesia during the first stage of labor without adverse maternal or fetal effects. 25 mg intrathecal tramadol with 2.5 mg bupivacaine had longer-lasting analgesia. The major side effect was vomiting.