The distribution of serum alpha 1-protease inhibitor (PI) or alpha 1-antitrypsin (alpha 1AT) subtypes was determined by thin-layer isoelectric focusing in a group of 1233 individuals from six Mongoloid populations of East Asia and Dravidian Indians. The sample comprised 385 Chinese from Singapore and 151 Chinese from the Fujien province; 126 Malays; 243 Filipinos; 112 Thais; 56 Koreans and 160 Dravidian Indians. The frequency of PiM1 ranged from 0.65 in the Thais to 0.81 in the Fujien Chinese. The highest frequency of PiM2 was found in the Dravidian Indians (0.28) followed by the Thais (0.25). The frequency of PiM3 was found to vary from 0.03 to 0.07 in these populations. A low frequency of PiF (0.01 to 0.02) and PiS (0.01 to 0.04) was also observed in the Mongoloid populations but absent in the Indians. The PiZ allele was completely absent in all these populations. The phenotypic distribution of PI subtypes was at Hardy-Weinburg equilibrium in all the populations.