Eleven biopsy specimens of normal skin and twenty-four biopsy specimens of psoriatic lesions were examined histochemically by using several lectins (Ulex europaeus, UEA-1; Dolichos biflorus, DBA; Bandeirea simplicifolia, BS-I; Concanvalia ensiformis, Con A; Triticum vulgaris, WGA; Ricinus communis, RCA; Arachis hypogoea, PNA) in order to evaluate the presence and distribution of various carbohydrates in normal and psoriatic keratinocytes. The findings revealed that keratinocytes from psoriatic lesions are distinguished by a different composition of carbohydrate residues incorporated in their plasma membranes. In particular, the intracellular transport of alpha-L-fucose, alpha-D-mannose, and alpha-D-glucose to the plasma cell membrane is impeded, whereas their synthesis in the cytoplasm of the psoriatic keratinocytes is largely unaltered. In addition, due to the lack of terminal alpha-L-fucose, the alpha-D-N-acetyl-galactosamine and alpha-D-galactose residues cannot be transferred to the plasma membranes and, therefore, the antigens for blood groups A and B remain incomplete in psoriatic epidermis. On the basis of these findings and in comparison with previous findings of our group on hyperproliferative, malignant keratinocytes, it is concluded that particularly the disordered cytoplasmic transport of alpha-L-fucose-carrying glycoconjugates may represent a specific defect in psoriasis, possibly linked with the pathogenesis of this disease.