Chromogranins A, B and C, proteins that are costored and coreleased with peptides and amines, have been identified in a variety of endocrine and nervous tissues, both normal and neoplastic. We examined the secretion of chromogranin A and chromogranin A + B by hormone-producing tumors in patients with endocrine pancreatic tumors (EPT), carcinoid tumors, pheochromocytomas and small cell lung cancer (SCLC). Radioimmunoassay (RIA) of the plasma/serum concentrations of chromogranin A + B showed a greater sensitivity than RIA of chromogranin A alone. All patients with EPT, carcinoids and pheochromocytomas had increased levels of chromogranin A + B, whereas a small number of the patients (5/18 with EPT and 1/3 with pheochromocytomas) had normal levels of chromogranin A. Also in immunocytochemical stainings, our polyclonal antiserum detecting both chromogranin A and B showed a greater sensitivity than other available antisera against chromogranin A, B and C.