HB 699 is a hypoglycemic agent that has a structural similarity to glibenclamid but does not contain the sulfonylurea group. We have studied the effects of HB 699 and the sulfonylurea glipizide on pancreatic polypeptide (PP) and insulin secretion in the dog. Both HB 699 and glipizide stimulated insulin release and caused hypoglycemia in normal dogs. The secretion of PP was stimulated by HB 699 before the onset of hypoglycemia, whereas, following glipizide administration, PP secretion increased only after the onset of hypoglycemia. As expected, in alloxan-diabetic dogs neither substance affected plasma insulin or blood glucose levels. There was, however, a stimulation of PP secretion by HB 699 that was not observed with glipizide. It appears therefore that HB 699, in contrast to glipizide, stimulates PP secretion in the absence of any changes in circulating glucose and insulin concentrations. The direct action of HB 699 on the pancreas was shown by stimulation of insulin and PP secretion in the in vitro perfused uncinate process. In view of its direct pancreatic actions, HB 699 may prove a useful tool for further study of PP secretory mechanisms.