The mosaicism of X-chromosome inactivation results in heterozy- gous G-6-PD-deficient females manifesting a wide variety of G-6-PD activity, ranging from normal to true deficient. Our results demonstrat- ed that heterozygous G-6-PD-deficient females exhibited either normal or deficient G-6-PD activity with 50% of the latter within the range of deficient homozygotes (Table 2). This may explain why there is no statistically significant difference between enzyme activity of G-6-PD- deficient homozygous and heterozygous females. In the G-6-PD- normal group, 7 out of 8 samples with normal G-6-PD activity were heterozygous for G-6-PD Viangchan, the remaining for G-6-PD Canton, whereas among heterozygous females with G-6-PD deficiency, no