OBJECTIVE: This open label, multicentre study was designed to evaluate the efficacy and tolerability of lanreotide Autogel (L-Autogel) in acromegalic patients over a 24-week period. The outcome of treatment with this new, long-acting, aqueous formulation of lanreotide was also compared with the patients' previous treatment with octreotide long acting repeatable (LAR). DESIGN AND METHODS: Twenty-five acromegalic patients (13 males, mean age 51+/-12 years) were switched from octreotide LAR (20-40 mg/4 weeks for at least 6 months) to L-Autogel, given deep subcutaneously at a fixed dose of 90 mg/4 weeks. After 12 weeks, the dose of L-Autogel was titrated according to patients' mean GH and IGF-I levels at week 8. It was increased to 120 mg/4 weeks if GH>2.5 microg/l or if IGF-I was above the age-adjusted normal range. It was reduced to 60 mg/4 weeks if mean GH<1 microg/l and IGF-I was within the normal range. If the values did not fall within these ranges, the dose remained unchanged at 90 mg. RESULTS: After 24 weeks of treatment with L-Autogel (final doses 60 mg in 3 patients, 90 mg in 4 patients and 120 mg in 18 patients), mean serum GH (2.9+/-2.4 microg/l) and IGF-I concentrations (332+/-193 microg/l) remained statistically unchanged when compared with baseline values under octreotide LAR (GH 2.4+/-1.8 microg/l and IGF-I 337+/-201 microg/l, non significant (NS)). There was a significant improvement of the acromegalic symptom score over the study period, from 4.8+/-3.4 to 2.8+/-2.5 (P<0.001) and a small but significant reduction in the residual pituitary tumour volume (P<0.05). Local side-effects were observed less frequently and no technical problems were encountered with the L-Autogel injections, as opposed to treatment with octreotide LAR (60 difficult injections/150 (P<0.001)). CONCLUSIONS: L-Autogel appears to be as effective as octreotide LAR in lowering GH and IGF-I concentrations in acromegalic patients. This treatment was also well tolerated by the patients, giving fewer local side-effects and technical problems with injections. These advantages may improve the long-term acceptability of medical treatment in acromegaly.