OBJECTIVE To investigate the possible beneficial effects of growth hormone (GH) in catabolic patients we examined the impact of GH on body fluid distribution in patients with ulcerative colitis undergoing elective abdominal surgery. METHODS Twenty-four patients (14 female, 10 male) aged 19-47 years were in a double-blinded study randomly assigned to receive either placebo (n = 12) or GH (n = 12) 6 i.u. s.c. twice daily from 2 days before until 7 days after ileo-anal J pouch surgery. Extracellular and plasma volume (ECV, PV) were determined using 82Br and 125I albumin dilution at day -2 and at day 7, and body composition was estimated by dual X-ray absorptiometry and bioimpedance. Changes in body weight and fluid balance were recorded and hence intracellular volume was assessed. RESULTS During placebo treatment body weight decreased 4.3 +/- 0.6 kg; during GH treatment body weight was constant (P < 0.01). There was a positive fluid balance in the GH-treated patients compared to the placebo group (GH: 3.6 +/- 0.7 l; plc: -0.7 +/- 1.2 l, P < 0.01). ECV increased 2.12 +/- 0.70 l during GH and was unaffected during placebo (P = 0.02). PV was unchanged by GH and decreased 0.39 +/- 0.08 l during placebo administration (P = 0.03). Intracellular volume (ICV) decreased less during GH than during placebo (GH: -1.42 +/- 0.45; plc: -3.70 +/- 0.76; P = 0.02). Bioimpedance remained constant during GH administration and increased 60 +/- 9 ohm in the placebo-treated group (P < 0.05). Plasma renin and aldosterone remained unchanged in both study groups. CONCLUSIONS Body weight, plasma volume and intracellular volume is preserved during GH treatment in catabolic patients and ECV is increased. From a therapeutic point of view these effects may be desirable under conditions of surgical stress.