• Sixty-nine growth hormone—deficient patients were treated for 1 year with somatotropin (recombinant DNA-derived human growth hormone) produced in mouse cells. The growth velocity of the 50 patients (72%) in whom the effectiveness of this growth hormone could be evaluated increased from a mean (±SD) 3.5±1.1 to 8.7±1.6. cm/y. An enhanced rate of weight gain was also observed. Bone age was not unduly accelerated. One of 66 patients developed antibodies to recombinant growth hormone, which did not affect the response to therapy. No patient developed antibodies to host cell proteins. An increased insulin response to a standard glucose load, without any change in glucose tolerance, was observed after 1 year of treatment. This authentic sequence human growth hormone preparation produced in mammalian cells is both effective and safe in the treatment of children with growth hormone deficiency.