Carcinoembryonic antigen (CEA), which is a well-known marker for the normal sweat gland apparatus and its neoplasms in the skin, was recently demonstrated in sebaceous neoplasms. The aim of this study was to examine the expression of CEA and related antigens in the other cutaneous keratinous neoplasms and verruca vulgaris. Normal adult skin, squamous cell carcinoma (SCC), senile keratosis, Bowen's disease, basal cell carcinoma (BCC), seborrhoeic keratosis and verruca vulgaris were stained immunohistochemically with a panel of monoclonal and polyclonal antibodies that recognize different epitopes of CEA and related molecules. Localization of the antigens was compared with that of involucrin and proliferating cell nuclear antigen. The strongest expression of CEA-related antigens, other than non-specific cross-reacting antigen (NCA) -50/90, was seen in SCC and verruca vulgaris, while no detectable expression was seen in BCC. Senile keratosis, Bowen's disease and seborrhoeic keratosis showed the predominance of the CEA-related antigens over CEA weakly expressed. Strong expression of both CEA and NCA-50/90 was seen only in SCC. All the expressions were limited to the cells situated in the upper epidermal cell layers of the tumours, at the centre of tumour islands in SCC and along the pseudohorn cysts in seborrhoeic keratosis, where involucrin was coexpressed. We suggest that CEA and related antigens are not only markers for sweat gland differentiation in the skin, as currently accepted, but are also expressed in various cutaneous keratinous neoplasms and verruca vulgaris. The expression may correlate with the terminal differentiation of the tumour cells, the strong coexpression of CEA and NCA-50/90 may correlate with the malignant potential of the tumour types, and the mechanisms that control the expression of CEA and related antigens in the neoplasms may be similar to those operative in verruca vulgaris.