The lectin-binding properties of psoriatic epidermis were assessed using a wide range of lectins. Changes in these properties were found at all levels of differentiation in lesional tissue. There was no clear evidence for an expansion in the population of basal-type cells. Binding of some lectins demonstrated a normal basal-suprabasal boundary. Others bound closer to the dermal-epidermal junction than in normal tissue, and expression of certain normal suprabasal characteristics was found in the basal layer in psoriasis. These findings suggest that the detected changes in psoriatic glycoconjugates reflect a programme of differentiation which is altered rather than incomplete.