A prospective randomized study of 267 pregnant women was undertaken to compare the efficacy of a pharmacy-prepared 3-mg prostaglandin E2 (PGE2) vaginal suppository with a 3-mg PGE2 vaginal tablet for induction of labor and cervical ripening. No statistically significant difference in success frequency was found between the two groups, either on the first day (72% and 74%, respectively; p greater than 0.05) or on the second day (89% in both groups). There was an equal proportion of women requiring oxytocin augmentation in the two groups, but the slower releasing properties of the vaginal tablet were reflected in a longer mean induction--delivery interval of about 4 h for this group. In both the pessary and the vaginal tablet groups, women who had not gone into labor on the first day showed a statistically significant increment in the Bishop score on the morning of the second day. The frequency of cesarean section was the same in both groups, but instrumental deliveries were more frequent in the vaginal tablet group. It is concluded that PGE2 vaginal tablets--a chemically stable alternative to pharmacy prepared pessaries--appear to be effective as regards cervical ripening as well as for labor induction.