In recent years there has been an impressive surge of interest in the mecha- nisms which control the onset and the maintenance of labour. Much of it stems from a constant awareness that gestational age at birth is still an important factor in neonatal mortality and morbidity. Advances in the sensitivity and specificity of immunoassay, the discovery of the prosta- glandins, new skills in fetal surgery and chronic catheterisation in experi- mental animals have greatly stimulated further research in this area. In the meantime clinicians became continuously more aware that, despite consider- able...