In 100 clinically-normal women, labor was induced at term by low amniotomy and PGE2. The drug was administered by either the oral or the oromucosal route, the same incremental dose scheme (initial dose of 0.5 mg; hourly increment of 0.5 mg until adequate uterine stimulation or a maximum single dose of 3.0 mg) being applied. Both routes of administration had comparable efficacy and were equally safe. The incidence of abnormal monitoring findings (uterine hypertonus, transient bradycardia and dips II during the first stage; late decelerations, progressive and transient bradycardia during the second stage of labor) and of low Apgar scores were similar. Acid-base and lactate-pyruvate equilibria in mother and fetus were not influenced by the route of drug administration in parous women. In nulliparae treated with PGE2 by the oromucosal route, higher values were found for the fetal-maternal difference in excess lactate than in those given oral PGE2; however, this is probably of little clinical importance.