Although the lung is not usually considered a major target organ of sex hormones, epidemiological observations, studies of pulmonary neoplasms in laboratory animals, and investigations of carcinomas derived from other "nontarget" organs suggest that sex hormones may have a role in the pathogenesis of bronchogenic carcinoma. To confirm that estrogen (ER) and progesterone receptors are present in human lung cancers, 19 resected lung cancers were examined for receptors using a prelabeled sucrose gradient method. Three squamous cell carcinomas were positive for ER (greater than 6.9 fmol/mg cytosol protein). Three squamous cell carcinomas, two adenocarcinomas, and one small cell carcinoma were positive for progesterone receptors (greater than 6.9 fmol/mg cytosol protein). One tumor, a squamous cell carcinoma arising in a woman who smoked, had an ER level of 301 fmol/mg, a highly positive level even for breast cancers. These observations may provide a basis for adjuvant hormonal therapy in selected lung cancer patients.