The early and late effects of long-term octreotide treatment on body composition were investigated in seven acromegalic patients by whole body bioelectrical impedance analysis performed before and after 6 and 30 weeks of octreotide treatment (100 μg, three times/day). The findings were compared with those of 14 normal subjects matched for sex, age, height and weight. Total body water (TBW) and fat-free mass (FFM) were significantly higher (median 41.3 vs 34.6 l and 58.3 vs 51.4 kg, respectively; P<0.005 in both) whereas body fat (BF) was lower (21.1 vs 30.8 kg; P<0.05) in the acromegalic patients before the treatment than in the normal subjects. Average body weight initially decreased by 3 kg (P<0.01) after 6 weeks of treatment, but increased by 1 kg (P<0.01) during the following 24 weeks of treatment. After 6 weeks of treatment, TBW and FFM decreased markedly by 3.1 l (P<0.01) and 3.8 kg (P<0.01), respectively, whereas BF increased by only 0.2 kg (P>0.05). After another 24 weeks of treatment, TBW and FFM were decreased by only 1.1 l (P<0.01) and 1 kg (P<0.01), respectively, whereas BF increased markedly by 2.6 Kg (P<0.01), BW and FFM were normalized after 6 weeks of treatment whereas BF was normalized only after 30 weeks of treatment. The median value of waist-hip ratio increased from 0.72 (range 0.66-0.84) at baseline to 0.78 (range 0.69-0.88) (P<0.01) a value similar to that of normal subjects, after 30 weeks of treatment. These results show that TEW and FFM are increased whereas BF is decreased in acromegaly, and these alterations in body composition are reversed with octreotide treatment. TBW is returned to normal particularly in the early phase of octreotide treatment while the normalization of BF requires a longer time. Additionally, the increased waist-hip ratio suggests a redistribution of adipose tissue from the peripheral depots to the abdominal region.