The intravaginal application of prostaglandin E2 for preinduction cervical ripening has proved to be advantageous in the management of patients with an unfavorable cervix. The purpose of this double-blind randomized investigation was to compare the efficacy and safety of two methods of prostaglandin E2 delivery. Patients who were to have preinduction cervical ripening because of an unfavorable cervix (Bishop score less than or equal to 4) were randomly assigned to be given a single dose of prostaglandin E2 as either 2.5 mg of gel or a 3.0 mg "chip" intravaginally in a placebo-controlled manner. Sixty-nine patients received the active prostaglandin E2, 34 in the gel group and 35 in the "chip" group. The groups were similar in maternal age, race, parity, gestational age, and initial Bishop score. Both forms of prostaglandin E2 were easy to administer and helpful in priming an unfavorable cervix. The need for, duration of, and maximum dose of oxytocin were similar in both groups. Cesarean delivery because of failed induction occurred in 5 of 35 (14.3%) patients receiving a "chip" and 4 of 34 (11.8%) receiving the gel. However, patients receiving a "chip" experienced a 20% (7/35) incidence of hyperstimulation, compared with 2.9% (1/36) in those receiving the gel (p less than 0.05). The only case requiring immediate cesarean delivery because of intractable uterine hyperstimulation received a "chip." We conclude that both methods were effective for cervical ripening, but the lower incidence of uterine hyperstimulation seen with the gel would suggest that it is preferable to the "chip."