Growth retardation after renal transplantation (RTx) is generally attributed to prednisone (PDN) administration, although the exact mechanism is poorly understood. In a group of 19 growth-retarded post-RTx children, we studied the effect of alternate day (AD; n = 12) and daily (D; n = 7) PDN therapy (0.10-0.25 mg/kg.day) on 24-h plasma GH and cortisol profiles, once in group D and twice on successive days in group AD. The maximal plasma GH response to arginine provocation (ATT) and plasma levels of insulin-like growth factor-I (IGF-I), IGF-II, and serum IGF-binding proteins (IGFBP) were also determined. The pulsatile character of the 24-h GH secretion was sustained in all patients. However, mean GH levels were significantly lower as compared with published data for healthy children, corrected for pubertal stage and sex. The highest mean GH levels were found in boys and girls in late puberty. Group AD had similar 24-h GH profiles whether on or off PDN treatment, which did not differ significantly from the GH profiles observed in group D. The maximal GH response during ATT was greater than 10 micrograms/L in 57% of the children. Group D had significantly lower mean and maximal cortisol levels than group AD, but all patients had a normal diurnal variation. Plasma immunoreactive IGF-I and IGF-II, and serum IGFBP-1 levels were normal, but serum levels of IGFBP-3 were increased. A significant negative correlation was found between the glomerular filtration rate and serum IGFBP-3 levels. In conclusion, our findings indicate that growth-retarded renal allograft patients, receiving either alternate day or daily PDN therapy, have decreased GH secretion, but a normal diurnal rhythm of GH and cortisol secretion as well as normal plasma IGF-I and -II levels. However, growth retardation after RTx may not solely be the result of decreased GH secretion. Renal graft impairment together with decreased IGF bioavailability may, in addition to the presumed direct effects of PDN on cartilage, contribute to the growth retardation after RTx.