Glucose-6-phosphate dehydrogenase was purified from blood samples originating from 33 subjects living in the ‘Midi-Pyrenees’ region (Southwest France). Biochemical and electrophoretic characteristics of several enzymatic variants were revealed. The distribution of the mutations in the subjects studied gave the following results: (1) Mediterranean Gd(–) and Gd(–)A identified variants; they constitute the main part of our observations. (2) Two original variants confirmed by the WHO International Reference Laboratory, that is: Gd(–) Toulouse and Gd(+) Luz-Saint-Sauveur; the latter mutation did not produce any haematological disorder. Absence of chronic haemolytic anaemia as well as a high rate of favism could be found in the families studied. As it is generally observed in Mediterranean regions, Southwest France population is characterized by a certain heterogeneity in biochemical and genetic