BACKGROUND To compare the analgesic efficacy of remifentanil with meperidine and fentanyl in a patient-controlled setting (patient-controlled analgesia, PCA). METHODS Parturients (n=159) were randomly assigned to receive remifentanil (n=52), meperidine (n=53), or fentanyl (n=54). Pain scores and an observer sedation scores were assessed hourly. Fetal outcome was evaluated with Apgar score, cord blood gas analysis and the Neurologic and Adaptive Capacity Score. RESULTS Pain scores decreased in all groups, the decrease varying from mild to moderate, average pain scores remaining above 4.5 cm in all groups. Remifentanil PCA was associated with the greatest decrease in pain scores, but the difference was significant only at 1 h. Pain scores returned towards baseline over time; 3 h after the initiation of treatment, pain scores no longer differed significantly from baseline values in any of the groups. Significantly more parturients receiving meperidine crossed over to epidural analgesia. Overall satisfaction scores were higher with remifentanil, but remifentanil produced more sedation and itching. More periods of desaturation (Sa(o(2)) <95%) were observed during administration of remifentanil and fentanyl. There were no significant differences in fetal outcome between the three groups. CONCLUSIONS The efficacy of meperidine, fentanyl, and remifentanil PCA for labour analgesia varied from mild to moderate. Remifentanil PCA provided better analgesia than meperidine and fentanyl PCA, but only during the first hour of treatment. In all groups, pain scores returned to pre-treatment values within 3 h after the initiation of treatment.