Red cell glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-chromosomal-linked abnormality often associated with hemoiytic anemia. The G6PD variants obtained from 2 unrelated males, one associated with enzyme deficiency and history of hemoiytic jaundice, and the other associated with enzyme deficiency but no hemoiytic problems, were examined. Although the 2 subjects have no known consanguinity, the two enzymes could not be distinguished from each other in respect to their electrophoretic mobilities and kinetic properties, both exhibiting slower than normal anodal electrophoretic mobility, lower Km for G6P and NADP and higher rate of utilization of 2-deoxy-G6P and deamino-NADP. An unique double-banded pattern was observed in starch gel electrophoresis at pH 7.0 and pH 8.6. The variant is distinguished from all reported Gd variants, and it is designated Gd (-) Santamaria.