BACKGROUND Intrathecal sufentanil provides rapid-onset and complete analgesia for the first stage of labor. The dose required to produce this effect can be associated with maternal respiratory depression, hypotension, nausea, or pruritus. Because clonidine potentiates the analgesic effects of opioids without increasing their side effects, the authors wanted to determine the efficacy of low doses of intrathecal clonidine (15 and 30 microg) combined with sufentanil. METHODS Ninety-eight parturient requesting labor analgesia were studied. In a combined spinal-epidural technique, patients were randomly assigned to receive one of the following intrathecal solutions: either 15 microg clonidine (n = 10); 30 microg clonidine (n = 10); 2.5 microg sufentanil (n = 13); 5 microg sufentanil (n = 13); 2.5 microg sufentanil and 15 microg clonidine (n = 13); 2.5 microg sufentanil and 30 microg clonidine (n = 13); 5 microg sufentanil and 15 microg clonidine (n = 13); or 5 microg sufentanil and 30 microg clonidine (n = 13). Visual analog scores for pain, blood pressure, heart rate, sensory levels, incidence of nausea and pruritus, and motor blockade, and maternal and cord blood concentrations of clonidine were recorded. RESULTS Patients receiving 30 microg intrathecal clonidine with 2.5 or 5 microg intrathecal sufentanil had significantly longer-lasting analgesia (145 +/- 36 and 145 +/- 43 min vs. 104 +/- 35 for those receiving 5 microg intrathecal sufentanil alone). Clonidine levels were undetectable in maternal serum. CONCLUSIONS Thirty micrograms of intrathecal clonidine combined with 2.5 or 5 microg intrathecal sufentanil significantly increased the duration of analgesia during the first stage of labor without adverse maternal or fetal effects.