The expression of PCNA and AgNORs count or AgNORs' area in 86 cases of primary lung cancer and 10 cases of inflammatory pseudotumor were studied by S-P immunostaining of monoclonal antibody (PC-10) and image analysis system. The results showed that the proliferating index (PI) of PCNA positive cells was closely related to AgNORs count and AgNORs' area measured. Both were correlated with the histological type, and the TNM status, decreased with the increasing degree of histological differentiation. Survival analysis showed that the PI and the results of AgNORs image analysis in surgical patients who survived over 5 years were significantly lower than those who survived less than 3 years. The results suggest that immunostaining of PCNA and AgNORs image analysis are useful in judging the malignant degree and the prognosis of primary lung cancer.