The clinical, haematological, and some molecular genetic features of 17 Orissan Indian patients with sickle cell-beta+ thalassaemia (S beta+ thal) are described and compared with those in 131 Indian patients with homozygous sickle cell (SS) disease. Patients with S beta+ thal had higher Hb A2 levels, and lower mean cell volume (MCV) and mean cell haemoglobin (MCH) compared to SS disease but no other haematological difference of statistical significance. High levels of Hb F occurred in both genotypes and the alpha+ thalassaemia gene frequency reached 0.47 in S beta+ thal and 0.32 in SS disease. Clinically there were no significant differences between the genotypes indicating that the low levels of HbA (3-5%) in this condition were insufficient to modify the clinical features. The thalassaemic beta globin gene is inactivated by a G----C mutation at position 5 of the first intron of the beta globin gene (IVS1-5 G----C) in all cases. This finding should facilitate the introduction of a prenatal diagnosis programme aimed at the prevention of beta thalassaemia or S beta+ thalassaemia in that population.