The fetal hemoglobin in the affected members of three Greek families with the hereditary persistence of fetal hemoglobin has only γ-chains of the type with alanine in position 136. Although certain Negro families had been considered to have only this type of γ-chains in their fetal hemoglobin, further studies required that they be reclassified. Consequently, the Greek cases are the sole examples of this class among the heterozygotes for the hereditary persistence of fetal hemoglobin. In Greek double heterozygotes for β-thalassemia and the hereditary persistence of fetal hemoglobin, fetal hemoglobin is increased above the level of hemoglobin F in simple heterozygotes and γ-chains with glycine in position 136 become apparent. In these individuals, γ-chains with alanine in position 136 apparently derive from the chromosome for the hereditary persistence of fetal hemoglobin and are present in the hemoglobin F with γ-chains of both types from the chromosome for β-thalassemia. When these data are correlated with earlier knowledge of the genetic state of the Greek individuals, modifications of our previous ideas about deletions as the genetic basis of the hereditary persistence of fetal hemoglobin must be considered.