Abstract
Blood samples from over 70 pregnant women have been examined for the presence of four prostaglandins. Samples obtained from women not in labour at different gestation periods and at term contained no detectable amounts of prostaglandins. Prostaglandin F was present in samples of blood obtained during normal spontaneous labour. The appearance of this substance in the blood preceded the uterine contraction. Whether prostaglandins play a part in the process of normal labour is still conjectural.