Clinical and haematological findings of 164 Turkish beta-thalassaemic heterozygotes with increased Hb-A2 are presented. The series comprised of 19 children, 81 females and 64 males. The majority of these thalassaemic individuals were asymptomatic and only 4 of them had slight or moderate splenomegaly. The mean values of haemoglobin concentration, PCV, MCH and MCHC were significantly lower than those of the corresponding normal controls. Erythrocytosis was present in 33% of them. Hb-A2 values ranged between 3.8 and 6.1%, and between 3.8 and 6.5% as assessed by the methods of DEAE- or DE-cellulose chromatography, respectively. Hb-F was found to be above the normal range in 15.1%. It is established that beta-thalassaemia with increased Hb-A2 is the most frequent variety of thalassaemia in Turkey (80%) and both beta+- and beta0-thalassaemia genes were present in this country. The regional distribution of beta-thalassaemia in Turkey is also presented and the origin of beta-thalassaemia genes in Turkish people is discussed.