The distribution of serum transferrin subtypes was determined by PAG electrophoresis and isoelectric focussing in a group of 2288 individuals from 10 Mongoloid populations of East Asia. The sample comprised 857 Chinese from different localities: Singapore (239), Malaysia (228), Taiwan (265), Hong Kong (65), Fouzhou (60); Koreans (332), Filipinos (281), Thais (455), Malays (335) and Indonesians (28). The frequencies of TfC1 varied from 0.73 to 0.79 in the Chinese and from 0.76 to 0.83 in the other Mongoloid populations. TfC3 was observed at a frequency of 0.02 in the Koreans and Chinese from Fouzhou. TfDChi was present in a low frequency (0.01 to 0.03) in all the populations. A low frequency of TfB was also present in all the populations. The phenotypic distribution of transferrin subtypes was at Hardy-Weinberg equilibrium in all the populations.