The increased level of fetal hemoglobin in nondeletional hereditary persistence of fetal hemoglobin (nd-HPFH) is associated with several single base substitutions in the promoter region of either the (G)gamma- or the (A)gamma-globin genes. In this study, we report two new forms of nd-HPFH found in two unrelated Greek adults with high HbF production (8.6% and 10.2% respectively) and positive for the (G)gamma-158 C-->T substitution. Scanning by DGGE analysis and direct sequencing of the gamma-globin gene 5' promoter region revealed the presence of a (G)gamma-196 C-->T in the first case and an (A)gamma-201 C-->T in the second. These mutations seem to reactivate gamma-genes and cause their high expression in the adult period.