The distribution of the sugar residues in glycoconjugates along the mesonephric nephron of chick embryo from the 4th day of incubation till hatching has been investigated, by means of six different horseradish peroxidase-labelled lectins. ConA and WGA showed an ubiquitous presence of alpha-D-mannose and N-acetyl-D-glucosamine along the nephrons. SBA was found to be a specific marker of the proximal tubule. PNA and LTA reacted only for a short time at some sites during the considered period of incubation. Sialic acid was detected at the glomerulus in the podocytes, capillary wall and, with a lesser extent, in the mesangial cells. Significant changes of the glycosylation pattern of the glycoconjugates during the period of mesonephric activity and the period of involution were seen.