Eighty-three kidneys from autopsy cases, all more than 60 years of age, were used in the present studies. Three millimeter-thick step slices from all kidneys were embedded in paraffin, and serial sections from all blocks used for the immunohistochemical demonstration of Leu M1 (leukocyte membrane antigen) and LTA (Lotus tetragonolobus agglutinin) in cells of proximal convoluted tubular origin, and PNA (peanut agglutinin) and EMA (epithelial membrane antigen) in cells of distal convoluted tubular origin. The ABC staining method was used in all cases. A total of 65 renal cell adenomas found in 31 of the 83 kidneys consisted of 40 papillary, 20 tubular and 5 solid type lesions. The sizes of these renal cell adenomas were from 0.6 to 5 mm in diameter and compression of neighboring tissues was characteristic. Papillary renal cell adenomas were positive in their cytoplasms for Leu M1 and LTA in 7 cases and at their cell membranes for PNA and EMA in 33 cases. The respective figures for tubular renal cell adenomas were 6 cases for Leu M1 and LTA and 14 cases for PNA and EMA. All solid renal cell adenomas were positive in their cytoplasms for PNA and EMA. The immunohistochemical results thus indicated 13 of 65 lesions to have a proximal convoluted tubular cell origin and 52 to be possibly derived from distal convoluted tubules or collecting ducts. A role for metaplasia, however, could not be ruled out.