Fourteen acromegalic patients, half of whom had been unsuccessfully treated with surgery, radiotherapy, or bromocriptine, were given the somatostatin analogue SMS 201-995 parenterally as the sole therapeutic regimen after a single administration had demonstrated suppression of serum growth hormone (GH). An impressive and sustained clinical improvement was documented in all patients, including those in whom bromocriptine had failed; most marked was the decrease in soft tissue swelling and headache and an improved performance status. GH levels decreased each time SMS 201-995 was injected but returned to basal levels within 8 h in most of the patients. With chronic therapy, 24-h mean levels were significantly suppressed, and the GH stimulability of thyrotrophin-releasing hormone and growth-hormone-releasing hormone (pl-44) was markedly reduced. Discontinuation of SMS 201-995 therapy was associated with a return of symptoms and abnormal GH dynamics. The efficacy and safety of chronically administered SMS 201-995 in active acromegaly opens new horizons for its treatment.