The purpose of the present study was to clarify kinetic aberrations and premalignant and malignant lesions of oral mucosa. Epithelial hyperplasia (EH), mild and moderate epithelial dysplasia (ED), carcinoma in situ (CIS), and squamous cell carcinoma (SCC) were evaluated for histone H3 mRNA, p53 protein (P53), cyclin D1, and cyclin B1. A few cases were positive for P53 and histone H3, but rarely coexpressed both in EH and ED. In CIS and SCC, increased expressions of P53 and histone H3 were seen, and there were also many cases showing extensive co-expression of both. There were many cyclin D1-positive cases of EH and ED. In CIS and SCC, increased numbers of cyclin D1-positive and cyclin B1-positive cells were apparent, and these cells were distributed widely. In cases of CIS with co-expression for histone H3 and P53, there was increased and wide distribution of cyclin D1-and cyclin B1-positive cells. These features of CIS may indicate that cell proliferation is induced, and that zonal differentiation of stratified squamous epithelium is irregular as seen in SCC.