Somatostatin (4 micrograms/min, cyclic form) was infused for 24 h on six occasions in four patients with carcinoid ileal tumor and multiple liver metastases. During infusion, spontaneous flushes and/or diarrhea were markedly reduced with a return to the pretreatment pattern on the next day. Urinary 5-hydroxyindole acetic acid excretion and plasma gastrin were not significantly changed, whereas plasma insulin presented the expected decrease and rebound. These results confirm that carcinoid symptoms are somatostatin-sensitive but do not provide evidence that serotonin or gastrin play a major role in inducing these symptoms.