A stimulation test using 1 microgram growth-hormone-releasing factor (GRF 1-29 X NH2)/kg bodyweight was performed in children with familial short stature and in children with constitutional delay of growth and development. The GH secretion induced by this means was not different in these groups, but there was a difference in the response between normal children and children with idiopathic growth hormone deficiency (GHD). GH secretion after GRF administration was significantly lower in the GHD group than in the other groups. However, 6 of 24 patients with GHD responded to the test with a normal increase in GH (greater than 10 ng/ml), and 11 with an intermediate response (2-10 ng/ml). Thus, the test does not differentiate individual patients with defective growth hormone secretion from normal short children.