Attempts of incubating red blood cells of G6PD-defect carriers in 10 from 25 patients showed format in these blood samples is able under the elected conditions to suppress haemolysis, to reduce the numbers of Heinz's bodies and to enhance GSH-concentration. A more distinct efficiency could be observed in enzyme variants with instable temperatures and if kinetic properties had changed. Prevention of haemolysis is particularly suitable as a parameter because it will reflect all damages connected with an enhanced membrane permeability. The increase of GSH-concentration as an important equivalent of reduction in the metabolism of red blood cells may diminish the toxicity of damaging factors having an effect on oxidation. The number of Heinz's bodies is essential in those cases where oxidation products of haemoglobin are increasingly formed only under certain conditions of incubation. The findings allow a format therapy to be recommended for selected G6PD defects.