It is now commonly accepted that a variety of nonendocrine tumors are capable of elaborating one or more humoral substances that resemble well known, well-characterized, biologically active hormones or their prohor mone precursors or metabolic products (see 1-3 for reviews). These observations have promoted considerable interest in the potential of mass screening programs for early detection of malignancies. These programs would be based on measurement, generally by radioimmunoassay (RIA), of elevated concentrations of one or another of these hormonal forms in the circulating blood. Or such RIAs might provide objective measures of tumor responsiveness to various therapeutic procedures. This review considers the potential role of ACTH determinations in the diagnosis and management of patients with bronchogenic carcinoma since it is among such patients that ectopic Cushing's syndrome occurs most frequently (1).