A long-acting depot formulation of octreotide (Sandostatin LAR, Sandoz LTD) has been recently developed. Preliminary studies indicated that, in acromegalic patients previously controlled by Sandostatin 300-600 micrograms/day in 2-3 sc injections, the intramuscular administration of 20-30 mg of Sandostatin LAR achieved, during one month a similar control of GH hypersecretion. In the present study, the variations of plasma levels of octreotide, GH and IGF1 were followed during 2 months in acromegalic patients receiving a unique injection of 20 mg (n = 4) or 30 mg (n = 4) of Sandostatin LAR. Following Sandostatin LAR 20 mg i.m, the baseline values of GH (8.1 +/- 2.5 micrograms/l) and IGF1 (684 +/- 92 micrograms/l) were normalized after 2 weeks and remained into the normal range during the 28 following days. Similar results were obtained, after a 30 mg i.m administration of Sandostatin LAR. In this later case, the maximal inhibition of GH and IGF1 (1.3 +/- 1.0 micrograms/l and 392 +/- 266 micrograms/l respectively) lasted 2 months. These data showed that a monthly injection of Sandostatin LAR (20-30 mg) allowed a correct control of GH hypersecretion in this series of acromegalic patients.