• To determine if pharmacologic and physiologic tests are equally effective in the assessment of growth hormone (GH) secretory status, serum GH levels were measured during sequential tests with intravenous arginine infusion and insulin-induced hypoglycemia (arginine-insulin tolerance test [AITT]) and during sleep in 62 children, aged 2.1 to 17.3 years. Responses during AITT and sleep were concordant in 53 patients and discordant in nine patients. Arginine-insulin tolerance test results were consistent with the subsequent clinical course in 80% of the patients while nocturnal sampling was consistent with the subsequent clinical course in 93% of the patients. Thus, the failure of a normal serum GH response to pharmacologic stimuli is not always a diagnostic indicator of GH deficiency. Additional investigation of discordant GH responses to pharmacologic and physiologic stimuli may lead to a further understanding of the control mechanisms of GH secretion.