The role of dietary protein intake in the pathogenesis of progressive renal disease has been recently reexamined. Studies of both animal and humans with chronic renal disease have shown that restriction of dietary protein may slow the progression of the decline in renal function. This occurs because of a decrease in intraglomerular blood flow and pressure. The mechanism of this phenomenon is not known. The effect of protein intake on renal function is thought to be hormonally mediated. Since growth hormone can increase renal blood flow as well as GFR, we tested the hypothesis that the presence of growth hormone is necessary for the increase in glomerular filtration rate (GFR) seen after the ingestion of a protein meal. We evaluated the change in GFR after a standardized mixed protein meal in 13 patients with growth hormone deficiency. Neither basal creatinine clearance after an overnight fast (76 +/−17 ml/min/m2; mean +/−SD) nor maximum increment after a 50 g/m2 protein meal (33 +/−11 ml/min/m2) differed in these growth hormone-deficient patients from 16 normals controls (76 +/−18 and 30 +/−15 ml/min/m2, respectively). Twelve hours after an injection of exogenous growth hormone, 0.06 mg/kg up to a maximum of 5 mg, the GFR response to a protein meal did not differ from the pretreatment response (77 +/−19 and 32 +/−17 ml/min/m2, respectively). We conclude that the presence of physiologic amounts of growth hormone is not necessary for the GFR response to a standard protein meal.