A man who did not produce and beta-chains did not suffer from a severe beta-thalassaemia. He was heterozygous for Hb G Philadelphia. It has been suggested that this haemoglobin variant was associated with alpha-thalassaemia and that interaction between alpha-thalassaemia and beta-thalassaemia decreased the imbalance of alpha/beta-globin biosynthesis and thereby the severity of the beta-thalassaemic disorder. Association of Hb G Philadelphia and alpha-thalassaemia in this man and his family is now demonstrated using bone marrow and reticulocytes of the propositus and one of his sons and reticulocytes only of another son.