Sustained growth retardation in spite of a successful renal transplantation (RTx) is a serious problem for many pediatric allograft recipients. Biosynthetic growth hormone (GH) was given to 11 prepubertal children with severe growth retardation after RTx in a placebo-controlled double-blind study, assessing its effect on height velocity (HV), bone maturation, renal function, plasma IGF-I and IGF-II, serum IGF-binding proteins (IGFBP), and lipid and carbohydrate metabolism. Six months of GH (4 IU/m2/day s.c.) was either preceded or followed by six months of placebo. The patients underwent a full examination every three months. All children completed the study. Mean HV improved significantly with GH therapy (P < 0.0001), but there was also some improvement with placebo (P = 0.06). The GH-induced HV increment exceeded that of placebo by 2.9 cm/six months. Bone maturation was not accelerated. Acute renal graft rejection did not occur in any of the patients. 125I-thalamate and 131I-hippuran tests showed that mean glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) did not change significantly during GH therapy. GH caused a significant increase in IGF-I (P < 0.0001), which was far greater than the insignificant increase in serum IGFBP-3 levels (P = 0.16). Mean serum levels of total cholesterol, low density lipoprotein, apolipoprotein-A1 and -B, which are elevated at the start of the study compared with that of controls, did not change significantly during GH therapy. GH induced a significant increase in mean integrated plasma insulin levels during oral glucose tolerance test, without changing plasma glucose levels. Serum fructosamine and parathyroid hormone levels remained constant. Impressive HV increment can be achieved with GH therapy in children with growth retardation after RTx, without significant changes in renal function. Bone maturation appears unaffected, suggesting an improve final height.