199 patients were used in a double blind placebo controlled trial testing the efficacy of prostaglandin E2 3 mg pessaries in the induction of labour. The trial showed that prostaglandin E2 pessaries were effective in the induction of labour but that with only a 55% success rate the results were less than that quoted by others. It was felt that the success rate could be increased by either reducing the time interval between insertion of the pessaries or by using a slow release vehicle for the prostaglandin. Surprisingly no significant shortening in the duration of labour was found between the prostaglandin group and the placebo group, despite a significant increase in the favourability of the cervix in the prostaglandin pessary group. Also no factors were found which definitely distinguished between the success or failure of induction of labour using prostaglandin pessaries. It was felt that prostaglandin pessaries were a safe and reasonably effective method of induction of labour and that, with reduction in the time interval between insertion of pessaries or the use of a slow release vehicle for the prostaglandin, the efficacy would be greatly increased.