The role of sex hormones in the pathogenesis of lung cancer is still unknown. There are conflicting results regarding immunohistochemical detection of the estrogen and progesterone receptors expression in non small cell lung cancer. To clarify these discrepancies 32 samples of lung carcinoma tissues obtained by lobectomy or pneumonectomy were studied. Two monoclonal antibodies (6F11 and ID5) for estrogen receptor detection and one (1A6) for progesterone receptor detection were used. Eighteen adenocarcinoma and 14 squamous cell carcinoma cases were investigated. There were 11 women and 7 men with adenocarcinoma and 4 women and 10 men with squamous cell carcinoma. Weak (+1) nuclear estrogen hormone receptor expression was detected in only one specimen of a woman with adenocarcinoma and in one specimen of a man with squamous cancer. None of the 32 blocks of paraffin embedded specimens expressed progesterone receptor. The positive estrogen and progesterone receptors expression in cancer tissue is an important argument against the pulmonary origin of the unknown primary tumor.