SummaryA multiplicity of transferrin variants have been detected in the course of the biochemical aspect of the study of the genetic effects of atomic bombs. Variants obtained from the studies of 19,770 individuals in Hiroshima and Nagasaki were compared by polyacrylamide slab gel electrophoresis using three kinds of buffer systems with different pH values and thin layer polyacrylamide gel isoelectric focusing. The variants were compared on the basis of their relative mobilities and isoelectric points; seven types of fast-moving variant (B-variant) and nine types of slow-moving variant (D-variant) were detected, involving a total of 154 and 273 individuals, respectively. All the variants were identified as genetic variants by family studies. No variant differed in allele frequency between the two cities. The variants detected in this study were compared with variants detected in residents of Mie district (another Japanese population), Caucasoids, American blacks, and Amerindians. Six additional types of Bvariant and four additional types of D-variant, which had not been detected in Hiroshima and Nagasaki, were identified.