The study of 1,785 persons of different racial groups in Malaysia revealed that the haemoglobin X com ponent (earlier reported as leading to Hb H disease when combined with α-thalassaemia) is present in the general population in appreciable frequencies: 2.24% in 536 Malays; 0.66% in 607 Chinese; and 0.16% in 642 Indians. The gene responsible for the haemoglobin abnormality is inherited as an autosomal codominant gene. This slow-moving component may be the same or similar to those described in α-thalassaemia from Greece and Thailand and in Chinese from Jamaica and the US.