A growth-hormone-releasing factor has been characterised and sequenced from a pancreatic tumour removed from a patient with acromegaly. It is a 40-residue linear peptide. Synthetic human pancreatic growth-hormone-releasing factor (hpGRF-40), 1 microgram/kg bodyweight, was administered as an intravenous bolus to six healthy men. hpGRF-40 selectively stimulated growth-hormone secretion. Serum growth-hormone concentrations were increased within 5 min, reaching a peak between 30 and 60 min (20 . 4 +/- 6 . 5 ng/ml compared with 2 . 1 +/- 0 . 1 ng/ml after placebo). Serum levels of prolactin, thyrotropin, luteinising hormone, and corticotropin (measured indirectly through plasma cortisol) were not increased after administration of hpGRF-40. Similarly, the concentrations of blood glucose, plasma insulin, glucagon, pancreatic polypeptide, cholecystokinin, gastrin, gastric inhibitory peptide, motilin, and somatostatin were unaffected by hpGRF-40. There were no changes in blood pressure, pulse rate, or body temperature, and no side-effects were noted. The characteristics of this peptide fulfil many of the criteria required of the hypophysiotropic growth-hormone-releasing hormone. hpGRF holds promise for a new approach to the diagnosis and treatment of various disorders of growth-hormone secretion.