Growth failure is a psychosocial problem for many patients who have undergone renal transplantation. 18 adolescents (mean age 15.6, range 11.3-19.5) with severe growth retardation after renal transplantation were treated with biosynthetic growth hormone (GH) for 2 years. All received prednisone, administered daily or on alternate days, with azathioprine and/or cyclosporin A. 16 were blindly assigned to one of two GH doses (4 vs 8 IU per m2 per day). Growth, bone maturation, renal graft function, plasma insulin-like growth factors, serum binding proteins, and other biochemical parameters were checked regularly. Glomerular filtration rate and effective renal plasma flow were tested with 125I-Thalamate and 131I-Hippuran. Data on growth and glomerular filtration rate during GH treatment were also compared with those of matched non-GH-treated controls. Mean (standard deviation) increment in height after 2 years of GH was 15.7 (5.1) cm, significantly greater (p < 0.0001) than in matched controls, 5.8 (3.4) cm. Results were similar for the two GH dosage groups. Bone maturation was not accelerated. Glomerular filtration rate and effective renal plasma flow did not change significantly. The incidence of a > 25% reduction in glomerular filtration rate over 2 years was not significantly higher in GH-treated patients than in non-GH-treated controls (39% vs 32%, p = 0.97). Although a few patients had deterioration of graft function, we could not find a relation with GH treatment. Our results show that sustained improvement of height can be achieved with GH in severely growth-retarded adolescents after renal transplantation.