ABSTRACTTrypsin separation of the epidermis from the dermis was applied to 14 benign, premalignant, and malignant epithelial skin tumors. The three‐dimensional architecture of the undersurfaces of these tumors was clearly observed in all cases.Seborrheic keratosis showed network‐like structures in young lesions and a reticulated type of lesion, but showed sharply demarcated mass‐like structures in well‐developed lesions and an acanthotic type of lesion.Bowen's disease, Paget's disease, and senile keratosis exhibited coarse network‐like structures similar to each other accompanied by a general decrease in the amount of melanin pigment. Boundaries between these tumors and the surrounding epidermis were more or less irregular and gradual.In superficial basal cell epithelioma, interconnections between tumor‐cell nests were likely to exist.It is suggested that this method may fill a gap between macroscopic and microscopic findings, and that it is of considerable use for detecting invasive changes, for determining interrelationships between tumors and skin appendages, and for deciding ranges of surgical