In the two years after an ultrasound service was introduced at this hospital obstetric referrals for abdominal radiography decreased by over 55%. Most of these were for estimation of fetal maturity. Out of 349 such patients subjected to radiography in 1976, 176 had already been examined by ultrasound; in only four did radiography appear to influence management. We believe that if a satisfactory ultrasound scan is obtained before 30 weeks of gestation subsequent radiological estimation of fetal maturity is unjustified. Radiography may still be necessary, however, for diagnosing fetal abnormalities.