Ultrasonic scanning in patients with symptoms of threatened abortion occasionally revealed an echo-free area between the membranes and the uterine wall. The echo-free area was found in patients at 11 to 20 weeks gestation who had a live fetus and is believed to represent blood. Seven smaller haematomas of less than 35 ml gradually disappeared and the pregnancies continued until term. Three patients who had haematomas of more than 50 ml subsequently aborted or had a premature delivery.