In a randomized study, uterine activity patterns were characterized with a portable pressure-sensitive device in 40 nonlaboring women at term with an unfavorable cervix who were undergoing preinduction cervical ripening with prostaglandin E2. The prostaglandin E2 was inserted into the posterior vaginal fornix as a single dose of either a 2.5 mg methylcellulose gel (20 cases) or 10 mg controlled-release pessary (20 cases). Uterine activity monitoring began 1 hour before dosing and continued for 12 hours. For those treated with the gel, low-amplitude, high-frequency contractions began within the first hour, reached a peak within 4 hours, and initiated sustained high-amplitude contractions in 10 (50%) cases. With the controlled-release pessary, low-amplitude, high-frequency contractions had a slightly later onset, reached a peak between the fifth and eighth hours, and initiated sustained high-amplitude contractions in 18 (80%) cases. Uterine hyperstimulation occurred in two (10%) pessary cases, with no adverse effect after removal. We conclude that low-amplitude, high-frequency uterine contractions began with either method of intravaginal prostaglandin E2 delivery but led to sustained, high-amplitude contractions primarily with the pessary.