Involucrin(molecular weight 92000 daltons) is a soluble cytoplasmic precursor of the crosslinked protein envelope that appear late in the terminal differentiation pathway of keratinizing squamous epithelia. In normal epidermis, this protein is present in the maturing cells of the upper stratum spinosum and the stratum granulosum, but is abscent in the basal layer. In a recent study, immunohistochemical localization of involucrin was shown to be a specific marker for squamous differentiation and maturation in various tumors. The auther investigated the involucrin expression by an immunohistochemical study on its distribution in normal and neoplastic tissues of the larynx. The results were as follows : 1) Normal laryngeal tissues revealed homogenous cytoplasmic staining in the superficial layers and intermediate layers. 2) In epithelial hyperplasia groups, diffuse cytoplasmic staining was seen in the upper layers. 3) Focal staining was showed in the invasive carcinoma and the higher it differentiated, the stronger it stained. Results of this study suggest that involucrin is sensitive and specific marker for squamous differentiation, and staining patterns for involucrin may be helpful in distinguishing benign from malignant lesion.