Immunohistochemical methods were used to determine the expression of the lung resistance-related protein (LRP) in 87 cases of untreated non-small cell lung carcinoma. LRP expression was detected in 39 patients (45%). A significant correlation between LRP expression and tumor resistance to doxorubicin was found (p=0.03, Fisher's exact test). An inter-relationship between LRP expression and gender, age, stage, lymph node status and survival times was not observed. Furthermore, a relationship between LRP expression and proliferation (cell cycle phases, take rate of lung tumors in nude mice and cyclin A expression) was not detectable. However, a correlation of borderline significance was noticed between LRP expression and the patients' smoking habits. Carcinomas in heavy smokers (more than 30 cigarettes daily) were more frequently LRP-positive than carcinomas found in non-smokers (p=0.09, Fisher's exact test).