In 27 women, uterine activity in the third stage of labour was correlated with blood loss measured quantitatively during the same period of time. Myometrial activity was reflected by total intrauterine pressures measured using a Gaeltec catheter tipped pressure transducer inserted transcervically within 5 min of delivery of the placenta. Blood loss over the same 2-hour period was collected on absorbent paper and measured in the laboratory by colorimetric measurement of the haemoglobin content. As total uterine activity in the third stage of labour decreases total blood loss increases, but there is a poor correlation of uterine activity to total blood loss over the same period of time, probably because of biological variations in myometrial activity in normal women.