A total of 23 previously untreated and 28 previously treated GH deficient children were included for at least 12 months in a trial of recombinant somatropin, 0.1 IU/kg/day given by subcutaneous injection. All the children increased their height velocity over the pretreatment values, to nearly 11 cm/year, corresponding to a significant increase in height of 1 SD score for chronological age. The increase in height SD score for bone age was also statistically significant. No adverse effects were recorded, though one child experienced local itching and redness at the injection site which did not recur after a short cessation of therapy. One child developed detectable antibodies to recombinant somatropin, but the binding capacity was low and no clinical symptoms or growth attenuation occurred. Recombinant somatropin was shown to be safe and effective during the first year of therapy in children with GH deficiency.