There are significant differences in the frequencies of various blood group antigens between Taiwanese and Caucasians, and also in the frequencies of the corresponding alloantibodies. The most interesting discoveries concerning Taiwanese are: 1) The most common ABO subgroups are the B3 phenotype, followed by the Ael phenotype. 2) The secretory H-deficient para-Bombay phenotype (OHm), which results from mutations in five different h genes, is not uncommon. 3) The Le(a+b+) phenotype has a frequency of about 25% and the Le(a+b-) phenotype is absent except in a few of the indigenous groups. 4) Anti-'Mi(a)' is the most common clinically significant alloantibody causing intravascular hemolytic transfusion reactions and hemolytic disease of the newborn. 5) The incidence of the corresponding MiIII blood group phenotype varies among the different ethnic groups, ranging from 0% among descendants of mainland Chinese from north of the Yangste to 88.4% among the Ami tribe. 6) There is an almost complete absence of Di(a) and St(a) antigens among the indigenous populations, in contrast to incidences of greater than 2% among the Chinese ethnic groups. 7) Nearly all (99.67%) Taiwanese are positive for the Rh(D) antigen. Among those with Rh(D) negative phenotype, about 30% have a very weak Rh(D) positive phenotype (Del phenotype). Since the corresponding anti-D antibody is also rarely encountered, routine D typing is not necessary. 8) Some rare blood group phenotypes found in Taiwanese are the i phenotype associated with congenital cataract, DVI phenotype, Dc- phenotype, Jk(a-b-) phenotype, and Lu(a-b-) phenotype.