A new histochemical technique in which lectin-gold complexes are applied directly to thin and semi-thin sections of tissue was used to determine the distribution of Helix pomatia lectin binding sites in the proximal tubule of Rat kidney. Whereas a strong labeling was seen on the brush border and baso-lateral plasma membranes of convoluted tubules, the plasma membrane of cells from the medullary straight segment was unlabeled. Some profiles at the frontier between cortex and medulla had a mosaic of positive and negative cells. These results show, therefore, considerable segmental variation in the glycocalyx composition of Rat proximal tubules.