BACKGROUND: There are quite a few studies examining the relative efficacy of different doses of intrathecal sufentanil for labor analgesia. The authors designed this prospective, randomized, double blind study to compare the efficacy and side effects of 5 and 10 microgram intrathecal sufentanil. METHODS: Forty healthy, laboring, term parturients, in the active phase of labor participated in this study. In a randomized, double-blind fashion, patients received 5 or 10 microgram intrathecal sufentanil as a part of combined spinal-epidural technique. Scores of pain, itching, nausea, and sedation were taken on visual analog scales before and every 10 minutes after drug injection for one hour. We also recorded maternal blood pressure, respiratory rate and peripheral oxygen saturation during the same time period. RESULTS: Both doses of sufentanil provided adequate analgesia. Although 10 microgram sufentanil produced a slightly more profound analgesia, the duration of pain relief did not differ between the two groups. Both drug doses were associated with significant increase in itching. The 10 microgram dose was associated with more sedation and a greater decrease in arterial oxygen saturation (SaO2). CONCLUSIONS: Both 5 and 10 microgram intrathecal sufentanil provided adequate labor analgesia. Both doses were associated with increased spinal (itching) and supraspinal (sedation, respiratory depression) side effects, the intensity of which appeared to be more profound in the 10 microgram group.