Although the kidney was recognized as one of the radioresistant structures early in the twentieth century (1,2), nephritis, hypertension, degeneration, and other morphological changes resulting from masssive doses of local X-irradiation have been reported by several investigators (3-5). Antopol and Glaubach (6) observed kidney glomerular lesions in mice that received 600 R of whole-body X-irradiation. Using fractional irradiation at a rate of 600 R every other day for a total dose of 3.6 kR, Klapproth et al. (7) demonstrated an impaired renal function in uninephrectomized dogs. Similar results were obtained by Mendelsohn and Caceres (8), who exposed the single remaining dog kidney to a total dose of 3.78 kR. Furthermore, Concannon et al. (9) showed that depressed renal functions in the dog were proportional to various dose levels of local X-irradiation up to 3.1 kR. In rats, when the exteriorized kidneys were exposed to a single dose between 2.5 and 4.0 kR, urine flow, glomerular filtration rate, and renal plasma flow were unchanged 7 days postirradiation (10). Clinically, a minimal dose of 2.3 kR applied locally to both kidneys was shown to be necessary to produce renal failure (11). The pathological effects of such renal irradiation in patients were clearly described by Luxton (12). Since the kidney plays a major role in the maintenance of hemeostasis, it was our purpose to investigate renal functional and hemodynamic responses to whole-body X-irradiation in dogs.