The introduction of prostaglandins into clinical practice has been one of the most important advances in obstetrics and gynaecology in recent years. During the last decade obstetricians have become familiar with these drugs for inducing labour and for terminating second-trimester pregnancy. Within the last year their use has been extended, in association with antiprogestin, to first-trimester termi­ nation. Although the effectiveness of prostaglandins in these pharma­ cological roles is clear, their full potential has still to be explored, and much remains to be learned about their physiology. Prostaglandins playa central role in the initiation of labour. Further clarification of this role could lead to improvements in preventing or treating preterm labour, which still remains the most important cause of perinatal mortality in this country. Prostaglandins are also inti­ mately involved in the mechanism of menstruation. More detailed understanding of this role should lead to more effective treatments for menorrhagia and dysmenorrhoea. These substances also playa part in the mechanism of implantation, and further research in this area may lead to more effective therapy for infertility.