To elucidate whether CCK receptors exist in lung tissues and their precise cellular localization in the lung.CCK-AR and CCK-BR mRNA expression and cellular distribution in the rat lung were detected by highly sensitive method of in situ reverse transcription-polymerase chain reaction (RT-PCR) and conventional in situ hybridization.CCK-AR and CCK-BR gene positive signals were observed in bronchial epithelial cells, alveolar epithelial cells, pulmonary macrophages and vascular endothelial cells of the rats' lung by in situ RT-PCR. The hybridization signals of CCK-AR were relatively faint. By in situ hybridization, however, only the signals of CCK-BR but not CCK-AR were detected in the lung, and the positive staining was only found in vascular endothelial cells and macrophages.CCK-AR and CCK-BR gene were present in pulmonary vascular endothelial cells, macrophages, bronchial epithelial cells and alveolar epithelial cells, which play an important role in mediating the regulatory actions of CCK-8 on these cells.