We have studied, haemoglobin A2′ (A2 prime), a δ chain variant haemoglobin occurring in a small percentage of individuals of African ancestry. In heterozygotes, the percentage of haemoglobin A2′ was found to be slightly lower then the percentage of haemoglobin A2, suggesting that the variant δ chain is synthesized at a reduced rate. When quantifying haemoglobin A2 for the diagnosis of β thalassaemia heterozygosity, it is essential to add together the A2 and A2′ to give ‘total haemoglobin A2’. However, it not necessary to use a different reference range for total haemoglobin A2 in A2′ heterozygotes. When using microcolumn chromatography, A2′ was found to be measured with A2. On the high-performance liquid chromatography instrument studied, haemoglobin A2′ fell in the haemoglobin S window but its retention time differed from that of haemoglobin S.