Parenteral somatostatin has been used to suppress growth hormone secretion in acromegalic patients, but long-term treatment is hampered by its short half-life of a few minutes in the circulation. An octapeptide analogue of somatostatin (SMS 201-995) has recently been developed that has greater potency and selectivity in suppressing growth hormone than the native hormone. In this study somatostatin and somatostatin octapeptide infusions were compared in 13 patients with active acromegaly. The octapeptide had a longer duration of action in the suppression of growth hormone than native somatostatin. A twice daily dose of 100 micrograms significantly suppressed growth hormone during the day. Prolactin was not suppressed, even in hyperprolactinaemic patients, and suppression of insulin was of short duration. Two patients had diarrhoea, but this disappeared when treatment with the octapeptide was stopped. Somatostatin is known to suppress pancreatic exocrine function, and it is therefore important to look for evidence of malabsorption during long-term treatment with the octapeptide. Somatostatin octapeptide is therefore useful in the treatment of acromegaly, but evidence of malabsorption should be watched for; nonparenteral routes of administration need to be assessed.