A new variant of glucose-6-phosphate dehydrogenase (G-6-PD) has been discovered in Northern Italy, in the district of Ferrara. This variant is characterized by high decrease of red blood cell enzyme activity (less than 5% of normal), high affinity for G-6-P and NADP, increased utilization of deamino-NADP and 2-deoxy-G-6-P, and faster electrophoretic mobility in the buffer systems commonly used for the classification of the G-6-PD variants. The new G-6-PD type was never associated with clinical manifestations in any cases except neonatal jaundice in some of the newborns with this enzyme deficiency. The frequency of the new variant in the Ferrara district indicates that it has probably appeared in this area by mutation some centuries ago. It is suggested that this variant should be named G-6-PD Ferrara.