To investigate how growth hormone (GH)-releasing peptide (GHRP) and GH-releasing hormone (GHRH) interact in patients with short stature, we examined the acute effects of GHRH1-29NH2, GHRP-2, and the combination of GHRH1-29NH2 and GHRP-2 on GH release in children with GH insufficiency ([GHI] group A) and idiopathic short stature ([ISS] group B). Ten children with GHI (aged 11.8 +/- 1.1 years; height, -4.2 +/- 0.5 SDS) and five children with ISS (aged 11.1 +/- 1.2 years; height, -3.2 +/- 0.1 SDS) were studied. Intravenous bolus infusions of GHRH1-29NH2 (1 micrograms/kg), GHRP-2(1 microgram/kg), and GHRH plus GHRP-2 (each 1 micrograms/kg), were administered in a randomized order. Because of the variability of GH responses, results were analyzed by a nonparametric statistical method. Patients in group A showed low GH responses to both GHRH1-29NH2 and GHRP-2 stimulation: in only three of 10 and one of nine cases, respectively, were the peak GH levels above 5.0 micrograms/L. GH area under the curve (AUC) 90 minutes after GHRP-2 administration was slightly less than for GHRH1-29NH2 (179 +/- 150 v 214 +/- 68 micrograms/L.min, P = .06). In group B, GH responses to GHRH1-29NH2 and GHRP-2 were approximately of the same magnitude (1,943 +/- 819 v 1,981 +/- 887 micrograms/L.min, P = .9).(ABSTRACT TRUNCATED AT 250 WORDS)