We have used immunocytochemistry to identify the major primary adhesion molecule of the cadherin class in human kidney. In frozen sections of kidney, A-CAM was detected using the monoclonal antibody GC4 on the surface of renal tubular epithelial cells. Renal tubular epithelium did not express L-CAM. No cadherin reactivity was found on the glomerular epithelial cells. Cultured renal tubular epithelium was studied by immunofluorescence and immunogold methods. A-CAM was found at the contact points of adjacent epithelial cells, the phenotype of which was confirmed by the demonstration of cytokeratins using the antibody CAM 5.2. The A-CAM molecule in human kidney had an Mr of 130 kD in Western blotting experiments. These results lead us to conclude that A-CAM is the major cadherin of adult human renal epithelium.