Because it has been found that growth hormone (GH) treatment of GH-deficient adults is able to reduce the total fat mass, the present study was undertaken to investigate the effect of GH treatment in obese subjects. The investigation was a double-blind placebo-controlled crossover study in which nine obese females were treated with GH (0.03 mg.kg ideal body wt-1.day-1) and placebo for 5 wk. Body composition was determined by dual-energy X-ray absorptiometry, and the quantity of intra-abdominal adipose tissue was determined by CT scan. Lipoprotein lipase (LPL) activity was determined in fat biopsies taken from the subcutaneous abdominal and gluteal region. GH treatment significantly reduced the total fat mass from 40.5 to 38.4 kg (i.e., 5% reduction of the total fat mass; P < 0.01), whereas the fat-free mass increased from 50.5 to 53.5 kg (P < 0.01). In addition, GH treatment significantly reduced the intra-abdominal adipose tissue determined by CT scan (reduction by 7 +/- 0.3%; P < 0.02). CT scan performed at the level of the femur showed a 7% reduction in adipose tissue and a 5% increase in muscle volume in the GH group (P < 0.05). Thus no clear regional differences in the GH-mediated reduction of the adipose tissue mass were observed. GH reduced the LPL activity by approximately 50% (P < 0.01) in the adipose tissue. Finally, GH treatment significantly increased the level of plasma free fatty acids (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)