Proliferating nuclear antigen (PCNA) plays an important role both in the process of replication and repair of DNA. The aim of the carried out investigations was to find out if there was any correlation between the depth of malignant infiltration, invasion of lymph nodes, presence of metastases in extra-regional lymph nodes, the length of patients' survival, and the value of PCNA proliferating index analysed in biopsy specimens before the operation, taken from 60 patients with oesophageal squamous cell carcinoma. In the groups with advanced squamous cell carcinoma of the oesophagus the following statistic correlation was found between PCNA proliferating index and: invasion of lymph nodes--p < 0.04; degree of carcinoma progression--p < 0.01; and blood vessels infiltration--p < 0.001. The survival of patients with carcinomas of high (> 50%) and low (< 50%) PCNA index did not differ significantly. It results from the above investigations that high values of PCNA index may indicate the presence of metastases in lymphatic nodes and the degree of progression of oesophageal carcinoma.