Malignant transformation is often associated with alterations in the expression of normal differentiation markers, which may serve as intermediate end points in carcinogenesis and cancer prevention. To identify early changes in differentiation markers during head and neck cancer development, we examined the expression of cytokeratins (CK1, CK8, CK13, and CK19) and involucrin by immuohistochemical methods in surgical specimens from 29 head and neck squamous cell carcinoma patients that included, in addition to carcinoma, adjacent dysplastic lesions (17 cases), hyperplastic lesions (21 cases), and adjacent histologically normal tissues (15 cases) and in specimens from 31 subjects with premalignant oral lesions (e.g, oral leukoplakia) without cancer, CK13 and involucrin were detected in all specimens from the cancer patients, and no differences in their expression were found among the different histopathological group. CK8 was detected in only 2.7% (1 of 36) of adjacent normal and hyperplastic tissues but in 58.8% (10 of 17) and 75.9% (22 of 29) of dysplastic and carcinoma tissues. The corresponding figures for CK19 expression in adjacent normal, hyperplastic, dysplastic, and carcinoma tissues were 13.3, 70, 71.4, and 82.1%, respectively. The expression of CK1 was not related to the progression from normal to malignant. In the leukoplakia lesions, CK8 CK13, CK19 and involucrin were detected in 13.8, 100, 74.2 and 100% of the specimens, respectively. These results demonstrate that CK19 expression increases in hyperplastic lesions and continues to be expressed in dyplastic and malignant lesions, whereas CK8 expression in low in adjacent normal and hyperplastic tissues and increases only in dysplastic and malignant lesions. Thus, CK19 and CK8 could be markers of sequential premalignant changes in head and neck carcinogenesis.