Peripheral blood globin synthesis studies were done in 11 patients with δβ-thalassaemia trait, Hb S-δβ-thalassaemia or δβ/βº-thalassaemia from two black and two Caucasian families. All patients had elevated Hb F and normal or decreased Hb A2 levels and 10 had family studies confirming the diagnosis. In addition, four unrelated non-thalassaemic patients with elevated Hb F levels also had peripheral blood globin synthesis studies. The β/α specific activity globin synthesis ratios in the three blacks with δβ-thalassaemia trait were 0.60–1.04. In the four Caucasians with δβ-thalassaemia trait, the β/α ratios were 0.58–1.02. These results demonstrate a wide range of ratios overlapping those of normal controls (0.99 ± 0.06). The βs/α ratios in three blacks with Hb S-δβ-thalassaemia ranged from 0.66 to 1.00, similar to those of patients with δβ-thalassaemia trait. In the black patient with δβ/βº-thalassaemia, the γ/α ratio was 0.67. The β/α peripheral blood ratios in the four non-thalassaemic patients with elevated Hb F ranged from 1.00 to 1.1, similar to those of normal controls. These studies indicate that a decreased β/α ratio is not an invariable finding in δβ-thalassaemia in blacks or Caucasian patients and that globin synthesis data alone is insufficient to diagnose definitively heterozygotes for δβ-thalassaemia or to distinguish this trait from non-thalassaemic haematological disorders associated with a normal percentage of Hb A2 and an elevated level of Hb F.