Quantitative information about the three types ofγchains (AγT, AγI, Cγ) has been obtained for the Hb F from 285 normal Black babies, 172 babies with a Hb S or Hb C heterogeneity, and from 150 babies and older patients with the SS, SC, or CC conditions by means of a high pressure liquid chromatographic micro-procedure. The frequency of theAγTgene in the AA babies was 0.1035, while that in the SS patients was a low 0.0362. This lowAγfrequency in the SS POulation adequately explains the lower percentage (13.2%) of AγTheterozygotes among AS newborn babies as compared to 17.9% among AA Babies. The genotype with the AyT mutant in trans to theβSmutation is presumed to occur about three times more frequently than that in which the AyT mutant is in cis to theβSmutation. A study of family members of one SS patient who has an AyT homozygosity provided data supporting linkage of the AyT andβSanomalies in some Hb S heterozygotes.