The safety and efficacy of recombinant DNA produced human growth hormone in the treatment of growth failure in prepubertal children with idiopathic or organic deficiency of pituitary GH has been assessed. Five patients entered this clinical trial. They had never been treated with hGH, anabolic steroids or any medicine that affected GH and all of them were healthy without any chronic disease; except patient 1, who took a surgical operation for cerebellar astrocytoma at the age of 3. Each patient was treated with subcutaneous injection of recombinant somatropin (SAIZEN) at a dosage of 0.2 IU/Kg +/- 10% three times per week in the evening for 1 year. Typical catch up growth was observed. The height increased by between 6.3 and 15.1 cm and their mean growth velocity of 3.7 cm/yr prior to therapy increased to 11.1 cm/yr during one year of treatment. The annual change in bone age during the treatment with SAIZEN was 2.0 +/- 0.6 years in four patients, except patient 2 who showed different bone age (right hand 3.5 years, left hand 6.0 years). Anti-hGH antibodies were observed in patient 1, but the binding capacity was low (1:10), and no clinical symptoms or growth attenuation occurred. No side effects or laboratory abnormalities were noted throughout the clinical trial. In conclusion, recombinant somatropin has a growth promoting effect and low immunogenicity, and it is shown to be safe and effective during the first year of therapy in children with GH deficiency.