Evidence is growing that the carbohydrate portion of glycoconjugates is not merely an inert structural addition to the protein or lipid background, but is involved in normal and altered physiological processes. Conjugation of the potentially bioactive carbohydrate ligand to an inert labeled carrier generates the tools to histochemically monitor the presence of sugar receptors like lectins in tissue sections. In head and neck squamous cell carcinoma endogenous lectins have been systematically characterized by a selected panel of conjugates of such synthetic probes. In this investigation we provide evidence that the anti-neoplastic agents carboplatin and 5-fiuorouracil influence the expression of carbohydrate-binding receptors. In cases with a statistically significant alteration, an increasing loss of binding capacity from treatment cycle to cycle was observed in cytoplasmic areas. This means that the extent of binding of β-N-acetyl-galactosamine, cellobiose, galactose, and sialic acid was affected. The pattern of diminished binding capacity in nuclear structures encompassed β-N-acetyl-galactosamine, β-N-acetyl-glucosamine, sialic acid as carbohydrate part of the neoglycoprotein. Thus, exposure to certain chemotherapeutic agents clearly influences the capacity of tumor cells to mediate protein-carbohydrate interactions. Concomitant with the elucidation of the functions of such an interplay the significance of this down-regulation will be appare