Nine acromegalic patients (five females and four males), mean age 50 +/- 4 years, presented macroadenomas (N = 7), microadenoma (N = 1) or normal computed tomography scans (N = 1). Patients were treated with continuous subcutaneous infusion of octreotide (range 200-600 micrograms/day). Following a washout period of 7 days, the patients were injected im with 30 mg slow-release lanreotide every 10 days for the first month and then twice monthly. In case of elevated growth hormone (GH) levels at 3 months, the patients were injected every 10 days for the next three months. Plasma GH and insulin-like growth factor I (IGH-I) decreased in all patients during octreotide treatment. After 6 months of octreotide treatment, seven patients were considered as well controlled (mean 8 h GH < 5 micrograms/l, IGF-I normal) whereas in two patients the mean 8-h GH and/or IGF-I levels remained increased. Serum GH and IGH-I increased after octreotide withdrawal. In one patient, serum GH and IGF-I increased during slow-release lanreotide administration and injections were stopped after 45 days. After 3 months of lanreotide, three patients were well controlled while in five patients GH or IGF-I levels were not normalized. At 6 months, five patients were injected twice monthly and three patients had one injection every 10 days. Six patients were well controlled and in two patients the mean 8-h GH level remained increased. The pituitary tumor volume decreased by 20-30% in two patients during octreotide, as well as in one other during slow-release lanreotide therapy.(ABSTRACT TRUNCATED AT 250 WORDS)