The frequencies of deficiencies of glutathione reductase (GSSG-R), pyruvate kinase (PK) and glucose-6-phosphate dehydrogenase (G6PD) in a Spanish sample are presented. A total of 2,129 individuals was analyzed for GSSG-R, 1,636 for PK, and 1,066 (629 males and 437 females) for G6PD. Beutler's method was used. The frequencies obtained for these deficiencies were: GSSG-R, 0.09%; PK, 0.24%; and G6PD, 0.79%. The results are discussed.