Data for a total of 942 new cases of hypopituitarism, out of 3493 patients treated with recombinant human growth hormone (GH) for more than 1 year, have been analysed. The mean peak GH correlated well with clinical variables related to growth and was considered to be a good index of GH secretory capacity. Mean peak GH was correlated inversely with obesity (r = -0.253, p less than 0.01). The lower the height velocity before treatment, the mean peak GH and the height SDS, the greater was the therapeutic effect achieved. The patients with mean peak GH less than or equal to 5 ng/ml were defined as having complete GH deficiency (GHD), and those with a mean peak GH of 5-10 ng/ml as having partial GHD. The clinical entity of GH neurosecretory dysfunction could not be identified from either the clinical variables examined or the therapeutic effect. The appearance of GH antibody was considered to be of no clinical significance because its incidence and titre were both low.