Bombesin-related peptides (BRP), a family of neuropeptides showing carboxy-terminal homology with the amphibian bombesin, are present in humans in many body systems (CNS, lung, gastro-intestinal tract) with a variety of biological activities. In the lung, BRP are mitogens for normal bronchial epithelial cells and fibroblasts, chemoattractant for monocytes and exert bronchoconstrictive activity. Increased levels of BRP have been described in the lung of cigarette smokers and in smoking-related diseases. Moreover appreciable quantities of BRP have been recently found in lysates of peripheral monocytes and alveolar macrophages of man and guinea pig. It has therefore been inferred that these peptides may play a role in the immunological function of lung tissue. The aim of this study was to determine the amount of BRP present in peripheral-blood mononuclear cells (PBMNC), monocytes and alveolar macrophages (AM) of normal subjects (n = 36) and chronic bronchitis patients (n = 36). Patients with chronic bronchitis showed a significant increase in BRP levels in all cell types (PBMNC, monocytes and AM) (p < 0.005) in comparison with normal subjects. In addition levels of BRP in monocytes and AM were found to be nearly four times higher than in PBMNC in both groups of subjects. We can therefore confirm previous observations concerning the presence of BRP in human cells of the monocyte-macrophage lineage. Furthermore our results demonstrate that BRP levels are increased in monocytes of chronic bronchitis patients and imply a potential role for these neuropeptides in lung immunological response in smoking-related diseases.