A survey of 46 patients with suspected growth hormone (GH) insensitivity is presented. Clinical details and plasma samples from these patients were analysed centrally. A diagnostic score based on basal levels of GH and insulin-like growth factor I (IGF-I), IGF-I response to GH (0.1 U/kg daily for 4 days) and height SDS was determined for all patients to identify those with GH insensitivity. A total of 29 such patients was identified (14 males and 15 females; age range, 3.2-22.6 years). Their mean height SDS was -6.0 (range, -8.9 to -2.6), mean weight SDS was -2.9 (range, -5.2 to 1.2). Pubertal development was delayed in three out of three boys and two out of six girls of pubertal age. Their basal GH level was 32.4 mU/l (range, 0.8-158.2 mU/l) and mean basal IGF-I level was 33.6 ng/ml (range, 20-97 ng/ml). None of the 29 patients showed a significant serum IGF-I response to injections of GH.