Human fetal haemoglobin (Hb F, o?ys) is a mixture of different molecular species. Two of them differ in position 136 of the 7 chain which is occupied either by glycine (G-r chain) or by alanine (*r chain) [l]. These chains are the products of two closely linked genes present in all normal individuals [ 1,2]. A variant of Hb F, Hb F Sardinia (ars$s 75 Ile + Thr) [3] is of unusual high frequency in various populations at birth [4,5]. Very recent results of peptide analysis suggested that the 775 Thr chain is a variant produced by the A7 locus [6,7] and corresponds to a genetic polymorphism. The study of this polymorphism is made difficult by the complexity of the methodology involved in peptide analysis [ 1,4,5]. In contrast, we report that isoelectric focusing (IEF) on acrylamide slabs using a shallow gradient of laboratory made ampholytes (pH 6.5-7.8) allows to separate Hb F 775 Thr from Hb F 775 Ile. It is a reliable and a simple method for the study of such polymorphism. We provide a direct evidence that the 775 Thr chain variant is produced by the A7 locus.