Background: Several clinical studies reported the efficacy of the long-acting SRIH analog, octreotide (Octreotide, Sandoz) in the treattnent of acromegaly. Recently, another SRIH analog (BIM 23014, Ipsen Biotech) was shown to decrease plasma GH levels in acromegalic patients. The recent availability of a long-acting formulation of BIM 23014 [slow release (SR) lanreotide] could avoid repeated sc injections or continuous sc infusions. The objective of this study was to determine the tolerability and effectiveness of the slow release (SR) somatostatin analog, SR lanreotide in active acromegaly. Method: Between March 1998 and May 1998, 10 patients were recruited in the prospective study carried out at Yonsei University. The effects of 6 weeks of SR lanreotide, given every 14 days at a dosage of 30 mg, im, were analyzed. All the patients completed the 6-week period of therapy. Results: SR lanreotide injection produced 45% suppression of area under the curve of GH levels from the basal value on oral glucose tolerance test(OGTT). GH values on OGTT were normalized (< 2ng/mL) in 30% of patients after 6 weeks, whereas insulin-like growth factor I (IGF-I) levels were normalized in 50% of patients. No correlation was found between pretreatment GH levels and GH response to SR lanreotide or between changes in GH and IGF-I during therapy, The significant differences in response to SR lanreotide were shown between the patients with residual mass and no visible mass. During treatment, there was the significant reduction in the percentage of patients complaining of joint pain, hyperhydrosis, and paresthesias. Changes in soft tissue swelling were documented by a significant decrease in the diameter of fingers. Mild diarrhea and fatigue were the most frequent side-effects (20 30%) when SR lanreotide therapy was started. However, these side effects decreased progressively. Significant changes were noted in carbohydrate tolerance. Conclusions: These data indicate that SR lanreotide at a dose of 30 mg, im, every 14 days is an effective treatment in most unselected acromegalic patients, especially in patients with no visible mass. Tolerability to SR lanreotide therapy is high. The use of a new sustained release formulation of somatostatin analog is clearly advantageous in improving patient compliance with medical treatment for acromegaly (J Kor Soc Endocrinol 14:472-482, 1999).