A population-based screening of newborns for the structural variants of fetal hemoglobin was carried out in Osaka Prefecture, Japan, by isoelectric focusing of globin chains using dried blood on filter paper. Of 80,000 newborns, 18 had α globin variants and 55 had γ globin variants. The incidence of γ globin variants (1/1,455) was much higher than that of α globin variants (1/4,444). Structural studies were then carried out on the abnormal γ globins in 36 samples, and revealed that 25 of them were Hb F Yamaguchi (AγT 80 Asp→Asn). The prevalence of this variant in Japanese was estimated to be as high as one per 2,100.