Ten patients with idiopathic pituitary dwarfism were treated with methionyl human growth hormone (met-hGH) produced by recombinant DNA technology. They were given 0.5 IU/kg/week of met-hGH for three months. There were no significant changes in physical, blood, urine examinations. Their height increased between 1.5 and 2.7 cm during the 3 months of treatment, which was calculated to be equivalent 6.0 and 10.8 cm per year with a mean increase of 8.7 cm. Anti-hGH antibody was observed in all patients between one and two months of treatment with a titer between 10(1)X and 10(4)X. In spite of the formation of antibodies, the growth rate did not decrease in 7 of the 10 cases.