Renal glucose titration studies were carried out in eight pregnant women with renal glucosuria and six female controls. it could be shown that the kinetics of renal glucosuria in pregnancy are very similar to familial renal glucosuria of type A. The tubular maximum of glucose reabsorption was lowered in our pregnancies to about the half. The data obtained clearly indicate that the renal threshold for glucose can be lowered significantly in humans by a still unknown endogenous factor.