Primary lung carcinomas often carry mutations in the p53 tumor suppressor gene. Most of these mutations alter the conformation of the p53 protein into a more stable phenotype that makes it immunohistochemically detectable. Asbestos is a carcinogen that can cause deletions in chromosomes and possibly also gene mutations. In this study we examined 70 primary lung carcinomas for p53 protein accumulation using a polyclonal antihuman p53 antibody, CM-1. Patients were interviewed about their occupational and smoking history and classified according to their anamnestical asbestos exposure. Presence of asbestos bodies (AB) was evaluated from histologic samples of peripheral nontumorous lung tissue using both 5-microns-thick sections stained with Perls' iron and 30-microns-thick unstained sections. Abnormal accumulation of p53 protein was found in 36 tumors (51%), more often in patients exposed to asbestos than in patients without exposure (67% versus 40%, p = 0.027). Significant association was also noticed between the accumulation of p53 and the asbestos content of lung tissue: 35% of the p53-positive patients had more than one AB/cm2 compared with 14% of p53-negative cases (p = 0.046). Patients with strongly p53-positive tumors were heavier smokers (57.2 +/- 38.2 pack-years) than patients with p53-negative or lightly positive tumors (38.9 +/- 19.9 pack-years) (p = 0.017). Our findings indicate that both asbestos exposure and heavy smoking can cause abnormal p53 protein accumulation suggestive of mutated p53.