Uterine performance (i.e., uterine activity expressed in Montevideo units and in pressure area, number, and amplitude of contractions) was monitored by intra-amniotic tocomanometry in 16 patients with lumbar epidural analgesia. Technically adequate recordings were obtained in 34 top-up doses of which 24 were given in oxytocin-induced or stimulated labor and 10 in spontaneous labor. Thirty-two doses of 10 ml. of 0.25 per cent and two doses of 6 ml. of 0.5 per cent plain bupivacaine were administered. Aortocaval compression was avoided by placing the patients in the lateral (31 doses) or the semirecumbent position (three doses). Statistical analysis by means of Student's test failed to show a difference in uterine performance before and after the top-up dose. It is suggested that aortocaval compression is an essential factor contributing to or responsible for the temporary depression of uterine activity that has been observed by other authors after epidural injections of local anesthetic agents.