7 out of 534 South Vietnamese males showed erythrocyte glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, giving a 1.31% incidence of G-6-PD deficiency. Partially purified erythrocyte enzyme was studied in 6 of the 7 G-6-PD deficient males. Three variants were found: G-6-PD Mahidol (3), Canton (2), and Long Xuyen (1).