The immunohistochemical phenotype, distribution and significance of proliferation of myofibroblasts in laryngeal epithelial hyperplastic lesions (EHL) and squamous carcinoma (SC) were analyzed. Samples of 42 resected larynxes and 40 laryngeal biopsies of EHL and SC were included. Immunohistochemistry was performed using antibodies against vimentin, alpha-smooth muscle actin (SMA), desmin and leukocyte common antigen. Myofibroblasts were vimentin- and SMA-positive, and were found exclusively in SC, indicating that invasion beyond the basement membrane is necessary to evoke a myofibroblastic stromal reaction. We observed two patterns of stromal reaction in SC: one was characterized by a marked proliferation of myofibroblasts and desmoplasia, with scarce lymphocytic infiltration; this pattern tended to be associated with well- or moderately differentiated SC. The other was characterized by few myofibroblasts, weak desmoplasia, and dense lymphocytic infiltration; the latter pattern tended to be associated with moderately or poorly differentiated SC. The degree of myofibroblast proliferation was inversely related to the density of lymphocytic infiltration. Antibodies against SMA also stained stromal blood vessels, demonstrating a gradual increase of vessel density as the grade of EHL increased. Immunohistochemical analysis of myofibroblasts provides useful information on the phenotypic characteristics of the stroma in laryngeal EHL and SC, and can serve as an additional marker of invasion.