The L1 antigen is a major cytosol component of human granulocytes that may also be expressed by macrophages and epithelial cells. Its epidermal and dermal occurrence was investigated in formalin-fixed routine biopsy material from eleven different inflammatory skin disorders. Localization was performed with a rabbit antiserum to L1 applied in an unlabeled antibody peroxidase-antiperoxidase method. L1 antigen was not found in normal skin except in epithelial cells of pilosebaceous units. However, epidermal L1 antigen was demonstrated in every biopsy specimen from lupus erythematosus, lichen planus, dermatitis herpetiformis, and atopic dermatitis, whereas granuloma annulare test results were usually negative. The occurrence of dermal L1 antigen depended on the composition of the inflammatory infiltrate; specimens rich in neutrophilic granulocytes (e.g., dermatitis herpetiformis) were particularly strongly stained. Extracellular dermal staining was also seen, especially in areas adjacent to accumulation of positive leukocytes. The varying epidermal occurrence of L1 antigen in skin diseases probably signified different degrees of proliferative activity of the epithelial cells and could apparently not be ascribed to uptake from the dermis.