Study of renal function in human pregnancy has many problems, one of them being the wide variation in absolute values among individual subjects. The only realistic way to investigate renal changes is to use each patient as her own control, that is, to perform serial studies on the same subject during pregnancy and in the nonpregnant state. This paper attempts to describe the changes that occur during human pregnancy in renal hemodynamics and in certain aspects of tubular function, particularly the handling of uric acid and glucose. The data are based on three serial studies performed between 1954 and 1959 and on a study published by William Dunlop in 1979.The increase in effective renal plasma flow during pregnancy appears to be considerably greater than previous estimates would allow. The maximum increments from nonpregnant values in the four serial studies range from 50 to 85 per cent. It seems that the increase occurs within the first trimester.