Polyacrylamide gel isoelectric focusing (PAGIEF) of EDTA plasma and neuraminidase-treated plasma samples at pH 3.5-9.5 containing 8.0 M urea followed by an electroblotting with enzyme immunoassay was applied for the detection of factor H (HF) phenotypes in 536 unrelated Japanese blood donors living in Tokyo. In the major cathodal components, phenotypes of HF were classified into three common and five rare patterns, and these were considered to be controlled by two common and two rare alleles. The data suggest that the HF*Q0 allele also exists in the Japanese population. Family studies confirm the hypothesis that the HF polymorphism is controlled by autosomal codominant Mendelian inheritance.