A European multicentre, open-label 12-month study with Sandostatin LAR administered intramuscularly at 4-week intervals was initiated in 151 acromegalics responsive to octreotide. All patients received 3 injections of the 20 mg dose, following which the dose was adjusted to 10 mg in patients with mean 4-hour GH serum concentrations below 1 microgram/L (N: 29) and to 30 mg in patients with concentrations above 5 micrograms/L (N: 22). The GH level suppression was significant in the 20 mg dose group (p < 0.01) and for all 151 patients (p < 0.004), and was consistently maintained in all patients for the duration of the study. The suppression of the mean serum GH concentration to below 2.5 micrograms/L was recorded in 69.8% of patients at the endpoint treatment with Sandostatin LAR and 65.8% during prior treatment with Sandostatin s.c. A consistent suppression of serum IGF-I levels was also achieved. The number of patients with headache, fatigue, perspiration, joint pains and paresthesias had decreased significantly (p < 0.05) after the 6t]h injection of Sandostatin LAR vs. previous s.c. treatment. No patient discontinued the study because of drug-related adverse events. The most frequently reported adverse events were mild diarrhea, abdominal pain and flatulence. The local tolerability was very good. No impairment of safety hematology, biochemistry and thyroid function tests and no increased incidence of gallstone formation was recorded. Well tolerated and at least as efficacious as the s.c. formulation, Sandostatin LAR might become an alternative primary treatment to pituitary surgery and radiotherapy.