A biologically active peptide designated hLCP has been isolated and purified to homogeneity from human lung carcinoma by means of acidic extraction and successive chromatography on Sephadex G-50, Toyopearl HW-40 F and reverse-phase high performance liquid chromatography columns. Analysis showed that peptide consists of thirteen amino acids. Primary structure of hLCP has been deduced by double-coupling Edman degradation combined with enzyme digestion as H-Ser-Pro-Pro-Asp-Gly-Lys-Lys-Glx-Ser-Ala-Asp-Val-Lys-OH. hLCP possessed significant excitatory activity on an electrical stimulation induced contraction. No hLCP could be detected in normal lung tissue. The possibility of using hLCP as a biochemical marker in the clinic for the early detection of lung carcinoma is being investigated.