A group of 11 pre-pubertal growth hormone deficient patients were treated with human growth hormone over a period of 4 years. In 6 of the patients the dosage was 4 IU 3 times a week and in 5, 8 IU 3 times a week. Changes in height demonstrated that the "catch up" was significantly greater and of longer duration in the second group. In spite of a more rapid increase of bone age in the second group, the prognosis of final height had improved significantly at the end of the study period. A comparative study of the plasma concentrations significantly at the end of the study period. A comparative study of the plasma concentrations of T4, TSH, gonadotrophins and steroids, to see if the greater velocity of bone maturity in the second group could be due to contamination of the preparation by other could be due to contamination of the preparation by other hypophysary hormones, did not demonstrate significant differences between the groups.