Sixteen patients with acromegaly have been treated with octreotide [ 100 µg twice daily to 200 µg 3 times daily according to growth hormone (GH) response] for between 3 and 44 months. The mean serum GH concentrations fell from 39.3 mU/1 before treatment to 10.5 mU/1 on day 1 of treatment and, with continued treatment (and higher doses in 8 of 16 patients), to 7.9 mU/1. In 2 patients there was no GH suppression. GH suppression after the first administration of octreotide appeared to predict long-term response. Pre-treatment serum insulin-like growth factor 1 levels were elevated in 11 of 12 patients investigated, but were normalized on continued octreotide therapy in 10 of 12. Octreotide suppressed prolactin secretion in all 6 hyperprolactinaemic patients. Steatorrhoea occurred in 15 of 16 patients at initiation of treatment, but resolved in all within 7 days. Two patients developed gallstones. In summary, octreotide is a safe and effective treatment for acromegaly, producing clinical and biochemical improvement in up to 90% of patients. Octreotide is a valuable adjunctive treatment where surgery has failed and also in those with contra-indications to surgery.