Recent advances now allow detection of the homozygous states of alpha- and beta-thalassemia in early pregnancy, thus giving couples at risk the option of early abortion. However, at the Prince of Wales Hospital, no reduction has occurred in the number of births of infants with haemoglobin Bart's hydrops foetalis. A survey by us has revealed a total of 33 cases during the 7-year period from 1987 to 1993. Antenatal records were available for 20 of the 33 and none of these showed that a thalassemia risk had been recognized prior to the development of hydrops. In some cases mothers had failed to attend antenatal clinics early in pregnancy. However, in others, there was apparent failure of vigilance on the part of the doctors concerned, because the thalassemia risk was not identified and appropriate referral for prenatal diagnosis was not made. During the same period, only five new cases of Cooley's anaemia were diagnosed, mostly after the first year of life. Antenatal records were unavailable for review.