We have carried out a prospective randomised study in 52 (46 male, 6 female) children with isolated growth hormone (GH) deficiency treated with a GH regimen of 15 IU/m<sup>2</sup>/week administered as a daily subcutaneous injection. At the onset of the pubertal growth spurt, the patients were randomised to receive either an unaltered regimen (26 males, 1 female) or 30 IU/m<sup>2</sup>/week (20 males, 5 females). There was no change in the frequency of GH administration. The number of females in this study was too small to give a meaningful result. In contrast, the boys treated with either dose regimen showed no significant alteration in growth rate, but there was a faster than normal progression in pubertal maturation. It is concluded that the optimum final height of children with isolated GH deficiency may not be achieved in patients without the therapeutic manipulation of the onset and/or duration of puberty. 16 short normal children (9 males, 7 females) were treated with GH in a regimen of 25 IU/m<sup>2</sup>/week (range: 20-30) as a daily subcutaneous injection. The mean age for the onset of GH treatment was 11.5 and 11.0 years in the boys and girls, respectively. Our data suggest that both boys and girls had a more rapid rate of pubertal maturation than normal. It may be that in terms of final height prognosis, the events of puberty related to GH treatment counterbalance the improvement in growth prognosis during prepuberty.