Members of a Jamaican family carrying the α-chain variant haemoglobin Hb Gα Philadelphia have been found also to show red cell abnormalities suggestive of a mild thalassaemia trait. Hb GαPhiladelphia differs from most other α-chain variant haemoglobins by being present in unusually high percentage in heterozygotes (Hb A + Hb Gα Philadelphia). It is proposed that the gene for this variant is linked with one for α-thalassaemia.