Glucose-6-phosphate dehydrogenase (G6PD) was partially purified from red blood cells of 44 Sardinian males with severe enzymatic deficiency and the variants characterized chromatographically and biochemically to see if there is genetic heterogeneity of the enzyme in Southern Sardinia. Three different variants associated with severe G6PD deficiency were identified: the common G6PD Mediterranean variant; G6PD Sassari, recently described by Testa et al. (1980), and a new variant that we have designated G6PD Cagliari. Family studies were carried out to demonstrate that these variants are due to the presence of different alleles.