In this study, we measured the expression of the mitogenic neuropeptide receptors for vasopressin (V1A), gastrin-releasing peptide (GRP), bradykinin (BK2) and gastrin by reverse transcriptase–polymerase chain reaction (RT–PCR), and show that GRP-receptor expression predicts sensitivity to SP-G in a variety of tumours (SCLC, non-small-cell lung cancer (NSCLC), colorectal, ovarian and pancreatic) in vitro and in vivo. The gene discussed is GAST; the disease is small cell lung carcinoma.