The present study evaluates the acute and chronic use of a long-acting somatostatin analog, octreotide acetate, in the treatment of patients with severe postgastrectomy dumping syndrome. In the acute phase, 10 patients with severe dumping were studied over 2 consecutive days before and for 3 hours after the ingestion of a 'dumping breakfast' in a randomized double-blind fashion. On one day octreotide (100 micrograms) was given subcutaneously 30 minutes before the test meal and on the other day an equal volume of vehicle was injected. An additional group of six postgastrectomy patients without dumping were studied in a similar fashion and these acted as controls. During placebo treatment the test meal resulted in an immediate increase (p less than 0.01) in the pulse rate and in plasma levels of glucose, glucagon, pancreatic polypeptide, neurotensin, and insulin. Similar changes were seen in the control group with respect to placebo; however glucagon and neurotensin (p less than 0.05) did not show the same magnitude of increase as seen with placebo. Treatment with octreotide acetate prevented the development of both vasomotor and gastrointestinal symptoms and completely ablated all of the above responses in plasma peptides. These changes were associated with complete ablation of diarrhea (p less than 0.001). Pretreatment with octreotide acetate completely suppressed the rise in plasma insulin response to the meal and this ablated the late hypoglycemia of dumping. Treatment with octreotide acetate resulted in delayed gastric emptying and transit time (578 +/- 244 minutes) versus 76 +/- 23 minutes with placebo and 125 +/- 36 minutes in controls (p less than 0.05). Chronic daily treatment with octreotide acetate resulted in minimal side effects. These patients demonstrated a stable fasting plasma glucose, normal liver function tests, and an average weight gain of 11% during a 12-month period. In addition most patients were able to resume employment. The long-acting somatostatin analog, octreotide acetate, is highly effective in preventing the development of symptoms of severe dumping syndrome, both vasomotor and gastrointestinal.