Plasma levels of immunoreactive parathormone (iPTH), immunoreactive calcitonin (iCT) and prostaglandins (PGE2) were measured by RIA in 115 patients with bronchogenic carcinoma. In 37 of these cases the following hormones were also assayed: adrenocorticotropic hormone (ACTH), cortisol, plasma renin activity (PRA), aldosterone, prolactin, human growth hormone (HGH), thyroid stimulating hormone (TSH), luteinizing hormone (LH), follicle stimulating hormone (FSH) human chorionic gonadotropin (HCG), progesterone (P), androstenedione (A), testosterone (T), estradiol (E2) and dehydroepiandrosterone sulphate (DHAS). High serum levels of many hormone-like substances and hormones were found and the levels of certain hormones varied in some cases according to the clinical evolution of the disease and the response to therapy.