Several neuropeptides have been shown to regulate the function of cells involved in immune response and inflammation. Neurotensin is a 13 amino acid neuropeptide localized primarily to the nervous system and gut. Neurotensin also stimulates mast cell degranulation and enhances phagocytic and cytolytic capability of macrophages, suggesting that this peptide regulates inflammatory and immune responses. Fibroblasts play an important role in inflammation and tissue healing, and these processes may be regulated by several neuropeptides that have been shown to bind to fibroblasts. However neurotensin receptors have not been identified on fibroblasts. Human embryonic lung fibroblasts (HELF) were examined for binding and biological effects of neurotensin. 125I-neurotensin binding to adherent and confluent human embryonic lung fibroblasts (HELF), plated in 12mm diameter wells was specific and saturable. Computer-assisted resolution of the binding data demonstrated two classes of binding sites: a high affinity, low capacity site (Kd = 1.6×10-11 M, 19.5×107 sites/well), and a low- affinity, high-capacity site (Kd = 10-8 M, 4×109 sites/well). Neurotensin stimulated immediate, transient, dose-dependent increases of cytosolic calcium in HELF (threshold dose: 1011 M), suggesting release of calcium from intracellular stores. The novel finding of neurotensin receptors on fibroblasts provides further support for this neuropeptide's role as a regulator of inflammatory and immune responses.