Initial year growth responses to single weekly injections of 2.5 units human growth hormone (hGH) in 29 patients with hypopituitarism (130 units/yr/patient) were compared to responses in a series using smaller doses in conjunction with androgen (48 to 112 units/yr); the US collaborative study experience with the standard dose (2 units 3 times/wk = 312 units/yr), and with two size-adjusted doses (0.06 units/kg 3 times/wk = 212 ± 94 SD units/yr, 0.03 units/kg 3 times/wk = 116 ± 33 units/yr); and to the British experience with much larger doses (1,040 units/yr). During the first year of hGH treatment our patients grew an average 13% faster than the androgen-supplemented and collaborative study-0.03 units/kg/dose groups. They had a similar pace to the collaborative study-312 units/yr and 0.06 units/kg/dose patients, but grew 15% more slowly than did the British patients. Growth response correlated positively with age and negatively with hGH dose per kilogram of body weight. Of 17 patients with isolated growth hormone deficiency ten developed hypothyroidism with hGH therapy, leading to a policy of routine adjunctive thyroxine replacement.