A new G-6-PD variant has been discovered in a 6-year-old boy, who is a carrier of a severe enzyme deficiency, with a typical favism background. The patient is of South Italian ancestry, and the enzymatic anomaly has been transmitted by the maternal grandfather. The enzyme is characterized by an elecrophoretic mobility slightly slower than that of the Mediterranean group variants (nearly 100%) with a normal affinity for G-6-P and NADP. The activity in red blood cells is very low (3% of the normal). The mutant enzyme is very unstable and its optimum pH is slightly biphasic. It shows an increased utilization of deami-no-NADP and 2-deoxyglucose-6-phosphate. Since this variant is different from those previously described, it has been named G-6-PD Toulouse.