Serum leptin decreases during growth hormone (hGH) treatment and pre-treatment values have been suggested as a predictor of the response to hGH in GH deficiency (GHD) but not in non-GHD syndromes. To investigate whether this holds true in children with chronic renal failure (CRF), we evaluated changes in serum leptin, insulin-like growth factor-I (IGF-I) and height before(b) and during the 1st year (3 months, 6 months, 9 months, 12 months) of hGH treatment (1 IU/kg per week) in 11 children (median age(b) 10.1 years, mean height(b) -2.9 SDS) with CRF. Serum leptin and IGF-I were compared with values from healthy children. Each patient also served as his/her own control, with values during treatment compared with those before treatment. Growth improved in all patients during treatment (mean change(12 m) +7.2 cm, change in height SDS(12 m) +0.5, P=0.001). Weight decreased (median decrease(12 m) 0.3 SDS, P=0.02) but body mass index (BMI) and serum leptin did not change during treatment. Serum IGF-I levels were low before (mean -1.1 SDS) but increased during hGH treatment, the increment being greatest at 10 days (mean increment +1.9 SDS, P<0.0001). Serum leptin(b) did not correlate with change in serum IGF-I(10d), height(12 m) or weight(12 m). Serum IGF-I SDS(b) correlated with height SDS at 12 months ( r=0.80, P=0.006) of hGH treatment. Serum leptin(b) correlated with BMI ( r(s)=0.75, P=0.01). Levels adjusted for BMI did not differ from values in healthy children and did not change during treatment. Despite an IGF-I and growth response during hGH treatment, serum leptin did not change and pre-treatment values did not predict the growth response in these children with CRF.