Five prepubertal children with previously untreated growth hormone deficiency were enrolled in this trial and treated with authentic recombinant human growth hormone hGH, 0.1 IU/Kg/day, subcutaneously, for one year. All of the children markedly increased their growth rate; the height velocity increased from 3.4 +/- 0.7 cm/yr to 11.3 +/- 2.0 cm/yr during one year's treatment. The height-standard deviation score for chronological age increased from -4.03 +/- 0.52 to -2.70 +/- 0.68. The bone age increased from 5.6 +/- 1.5 year before treatment to 6.4 +/- 1.6 years after one-year treatment. Only one child acquired low titer anti-hGH antibodies during the course of treatment (1:2 to 1:6). No untoward symptoms were complained of by these children and no biochemical abnormalities occurred except transient subclinical hypothyroidism in one child during the treatment course.