In nine Indian patients ranging in age between four and 61 years, with mild Hb SS disease and very high Hb F levels, theGγglobin chain levels of their fetal hemoglobin ranged between 64.0% and 70.0%, with a mean of 68.1% (S.D.±2.6) of the total amount ofγ-globin chains. Eight of the nine patients were homozygous for a specificβsgene haplotype #31. The other one was doubly heterozygous for the same specific haplotype and another haplotype, which differed from haplotype #31 by the presence of Bam HI site 3' to theβgene and absence of Pvu II site 5' to theψβgene. Theβgene organization studied by Pst I restriction enzyme analysis was found to be normal and the Xmn I site -158 5' toGYβgene was present in all patients examined.