To evaluate the efficacy, safety and tolerability of octreotide LAR (long-acting repeatable octreotide) in the primary therapy of acromegaly. Ninety-eight previously untreated acromegalics were recruited into this prospective multicentre study. A total of 68 patients successfully completed 48 weeks of the study period, received 12 doses of octreotide LAR 10-30 mg every 4 weeks, and constituted the population used for this analysis. A clinically relevant reduction (i.e. to < or = 5 microg/l) in mean GH (mGH) was recorded in 72% of patients after 24 weeks of treatment, and 42% reached a 'safe' GH value (< or = 2.5 microg/l). At week 48, 16 more patients were considered partial GH responders (GH > 2.5 microg/l and < or = 5 microg/l) and 44% had reached a GH level < or = 2.5 microg/l. IGF-1 levels normalized in 38% and 34% of patients after 24 and 48 weeks of treatment, respectively. At study completion, 10 patients (14.7%) who had not normalized their IGF-1 levels had achieved at least a 50% decrement in this marker. In eight microadenoma patients, tumour volume decreased from a mean baseline level of 298 +/- 145 mm3 to 139 +/- 94 mm3 after 24 weeks and to 99 +/- 70 mm3 after 48 weeks of therapy. In 60 patients with macroadenoma, the corresponding values were 3885 +/- 5077 mm3 at baseline and 2723 +/- 3435 and 2406 +/- 3207 mm3 after 24 and 48 weeks, respectively. At weeks 24 and 48, a significant (> 20%) tumour volume reduction was reported in 63% and 75% of patients, respectively. A reduction in the severity of symptoms of acromegaly was observed early in treatment and was maintained throughout the study period. Octreotide LAR represents a viable alternative to surgery for primary treatment of acromegaly leading to a progressive regression of tumour volume, a sustained control of biochemical abnormalities and an adequate relief of symptoms of the disease.