The purpose of this study was to determine if prostaglandin E2 (PGE2) in a controlled-release vaginal insert with retrieval system can produce cervical ripening at term. This was a multicenter, double blind, randomized, placebo-controlled study involving 206 patients with 102 receiving active agent. A successful outcome was defined as a change in Bishop score of > or = 3, or a Bishop score of > or = 6 at 12 h or delivery within 12 h of the insert placement. Analysis was by Fisher's exact test, Wilcoxon's two-sample rank-sum test, and Student's t-test where appropriate. One hundred ninety-three women completed the protocol. Initial Bishop scores were 2.6 +/- 1.2 and 2.5 +/- 1.4 in the PGE2 and placebo groups, respectively. The incidence of cesarean delivery was identical in the two groups. Uterine hyperstimulation lasted 2-13 min in 5 PGE2 patients (4.9%) with 1 patient requiring tocolysis. More patients in the PGE2 group had a change in Bishop score of > or = 3 (62% vs. 40%; P = 0.002), a Bishop score > or = 6 after 12 h (46% vs. 34%; P = 0.11), and vaginal delivery within 12 h (6.5% vs. 1%; P = 0.055). Sixty-five percent of PGE2 group patients had a successful outcome vs. 44% of control patients (P = 0.001). In conclusion, when administered in a controlled-release vaginal insert with a retrieval system, PGE2 is effective in promoting cervical ripening at term.