Skin blisters at different stages were taken from 4 patients with bullous pemphigoid and studied mainly by scanning electron microscopy. The under-surface of the roof of the newly formed blisters was composed of columnar or cuboidal epidermal cells. Their intercellular space was dilated. Most of the cells were degenerated and shed off into the blister fluid. The under-surface of the roof of the fully developed blisters was composed of flattened epidermal cells which were polygonal in shape. These findings suggest that the basal cells are degenerated and shed off into the blister fluid, so that the prickle cells become flattened and directly face the blister fluid during blister formation.