In an attempt to establish the reference pattern and the plasma growth hormone (GH) response to growth hormone releasing factor (GRF) (1-29)NH2, 5 normal stature with single kidney children and 14 with idiopathic GH deficient dwarfism received intravenous injections of 1 microgram/kg GRF(1-29)NH2. Plasma GH levels were measured at 0, 15, 30, 45, 60, 90, and 120 min after injection. The results showed that, first, in normal stature with single kidney children, each plasma GH reached peak level (80.31 +/- 19.28 ng/ml) at 45 min after injection. Second, the majority of those with GH deficient dwarfism also obtained maximal GH levels (13.10 +/- 10.78 ng/ml) at 45 min after injection but at significantly lower levels than the normal children (P < 0.01). To compare with that obtained after the insulin-induced hypoglycemia test, the peak GH level after GRF was higher but there was no significant correlation between them. The maximal GH level after GRF(1-29)NH2 injection did not show significant correlation with either chronological age or bone age. Third, 3 of 14 (21.4%) with GH deficient dwarfism had half response to GRF(1-29)NH2. It is reasonable to assume that out of these patients' GH deficiency is of hypothalamic origin. Therefore, GRF test is a safe and useful test for differential diagnosis of defect level in GH deficiency and may become a therapeutic regimen.