Adenocarcinoma frequency in Pu incorporation-related lung cancer patients among plutonium workers was found to be 74% versus 33% in control. Each histological pattern of lung cancer appeared to be related to several etiological factors but in varying degree. Incorporated Pu proved the strongest factor in adenocarcinoma development. Its odds ratio (OR) was 6.9, while that for smoking-4.3. However, smoking appeared to be the most significant factor in squamous cell carcinoma genesis (OR-6.8). Among other factors were chronic obstructive pathology of the lung (OR-3.9) and reduced body weight (OR-2.1). The OR for Pu incorporation was 3.9. Squamous cell carcinomas were traced to reduced body weight (OR-2.9), heavy smoking (smoking index more than 500) (OR-3.5). However, no significant relationship has been established between carcinogenesis and Pu incorporation.