We have analysed the alpha-globin gene defects present in several members of a large family from Southern Turkey. One deletional alpha-thalassaemia-1 (type MED-II) was found in 10 subjects; this deletion is in excess of 26.5 kb and includes all zeta- and alpha-globin genes. Besides the common types of deletional alpha-thalassaemia-2 (-3.7 kb and -4.2 kb) we observed a nondeletional alpha-thalassaemia-2 that results from an A --> G mutation (AATAAA --> AATGAA) in the polyadenylation signal of the alpha-2-globin gene; the same A --> G replacement is present in the psi-alpha-l gene. The mutation must cause a considerable alpha-chain deficiency as is evidenced by the haematological data for five members with Hb H disease due to a compound heterozygosity for alpha-thalassaemia-1 (MED-II) and the newly discovered poly A mutation. Several members had additional beta-chain abnormalities (Hb S, Hb D-Los Angeles, beta-thalassaemia); the 11 persons with a Hb S heterozygosity and various alpha-globin gene defects (-alpha/alpha-alpha; alpha(T)alpha/alpha-alpha, - -/alpha-alpha, -alpha/-alpha and - -/alpha(T)alpha) showed a decrease in the level of Hb S that was directly related to the severity of the alpha-chain deficiency.