Patients with acromegaly, who are not cured after transsphenoidal adenomectomy, may be treated with external irradiation and/or octreotide injections. Recently, a long-acting formulation of octreotide (Sandostatin LAR has become available in clinical practice. We assessed the effects of treatment with this long-acting octreotide in 18 consecutive patients with acromegaly treated in our center, who had persistent signs and symptoms of acromegaly despite transsphenoidal surgery with (n=7) or without irradiation (n=11). Twelve had already been treated with regular Sandostatin for a period of 0.5-8 years in dosages of 3 x 50 to 3 x 300 mcg s.c. (median daily dose 300 mcg). All patients started with i.m. injections of 20 mg Sandostatin LAR every 4 weeks. In the patients who started treatment with octreotide for the first time, mean serum IGF-1 levels (measured by IRMA, Nichols Diagnostics) decreased from 634+/-229 to 255+/-88 ng/ml after 3 months, 271+/-81 ng/ml after 1 year and 263+/-97 ng/ml after 2 years (all P<0.05), while random GH levels (DELFIA, Wallac) decreased from 6.6 (range 3.1-67.0) to 2.1 (0.5-3.1) mU/l after 2 years (P<0.05). In the 12 patients who had already been treated with octreotide, mean IGF-1 also fell, from 367+/-193 to 331+/-195 ng/ml (P=0.023) after 3 months, to 342+/-191 ng/ml after 1 year and 277+/-169 ng/ml (P=0.002) after 2 years, while random GH levels decreased from 4.5 (1.1-46) mU/l at baseline to 2.1 (0.4-23.0) after 2 years (P=0.003). Therefore, the average decrease of IGF-1 was 10% after 3 months and 25% after 2 years. One patient had a decrease of less than 5% (but her IGF-1 was normal, 193 ng/ml), and one patient showed no response to both regular and long-acting Sandostatin (ave. IGF-1, 755 ng/ml). No specific side-effects occurred. One patient chose to return to t.i.d. injection of regular octreotide because of slight worsening of her complaints of headache despite normal IGF-1 levels. All other patients favoured continuation of the monthly injections. In six patients, the dose had to be increased to 30-40 mg monthly because the IGF-1 levels still remained elevated. Sandostatin LAR may be considered a great improvement for the treatment of patients with (symptomatic) acromegaly.