Using PC 10, an antibody to proliferating cell nuclear antigen (PCNA) and a standard immunohistochemical staining the authors examined 11 cases of simple hyperplasia of epithelium (SHE), 32 cases of atypical hyperplasia of epithelium (AHE) and 42 cases of laryngeal squamous cell carcinoma (LSCC) for expression of PCNA, a protein associated with DNA polymerase dalta and DNA replication, a marker for tumor cell proliferation. The results revealed that PCNA indices in SHE, AHE and LSCC were 9.5%, 27.33% and 68.05%, respectively. The PCNA indices were 63.68%, 69.57%, 71.18% in the well, moderately and poorly differentiated LSCC, respectively, there were significant differences. The PCNA indices were 63.88%, 70.82%, 66.20% and 69.04%, respectively in stages I, II, III, and IV of LSCC; no significance was found. There was a strong negative correlation betwee survival time and the tumor cell proliferative activity (r = 0.6243). PCNA might provide a useful tool for studying cell proliferation in situ under normal and pathological condition.