A method of graded sieving for counting of glomeruli in removed kidneys is described. The number of nephrons (glomeruli) in six normal kidneys deriving from autopsies of three children 22–73 months of age was 1.82 ± 0.35 × 106. The results give a little higher number than most previous studies with which they are compared. In the kidneys of two 10- and 15-month-old patients with the congenital nephrotic syndrome of the Finnish type the mean number of nephrons was 3.17 ± 0.52 × 106 which is on the average 73 % higher than in the normal kidneys studied. The number of nephrons in kidneys of five other patients showed an average of at least 3.42 ± 0.30 × 106 the counting method being a little different. The unusually high number of nephrons in CNF kidneys seems to be fully