- GH deficiency due to pituitary or hypothalamic tumors or disease affecting this area. Subjects will have been treated with medication, surgery, radiation, or a combination of these. GH deficiency will be defined as a peak plasma GH of less than 5 ng/ml in response to insulin tolerance testing or growth hormone releasing hormone (GHRH) plus arginine stimulation test. In subjects with suspected hypothalamic dysfunction the arginine plus L-dopa stimulation test may be used, with a cutoff of 1.7 ng/ml for diagnosis of GH deficiency. Partial GH deficiency will be defined as a GH peak of 5 to 9 ng/ml (inclusive) during insulin tolerance testing or GHRH plus arginine testing.