In this study, determination of gastrin concentration in bronchoalveolar lavage fluid and serum has been detected by radioimmunoassay in 30 cases of lung cancer and 24 cases of non-cancer pulmonary diseases. The results show that the gastrin concentration and its positive rate of lavage fluids from cancer lung are much higher than those from healthy lung and serum in lung cancer patients, and those from serum and both disease and healthy lung in non-cancer pulmonary disease patients (P less than 0.01). The gastrin ratio of lavage fluids from cancer lung to serum is also significantly higher than the ratio of lavage fluid from healthy lung to serum and all the ratios in the non-cancer pulmonary disease group. These results suggest that there is a high gastrin concentration in local tissue of lung cancer, which is signified by the high concentration of gastrin and its high positive rate in lavage fluids from the lung with cancer. Therefore, the gastrin determination in lavage fluids and gastrin ratio of lavage fluids to serum are more reliable in the differential diagnosis of benign from malignant pulmonary diseases than gastrin determination of serum alone.