Secondary to the osmotic and diuretic effect of contrast material, normal kidneys increase in size similarly with either 25 or 50 cc. contrast material. Although distensibility seems maximal with 25 cc., larger amounts of contrast material cause increased flow rates, more distention of collecting systems, and better pyelograms. Although an oral water load can effectively wash the contrast material out of the kidneys, a lack of consistency makes an intravenous washout preferable. Those patients with abnormal changes in renal size and calyceal visualization time suggest that other factors, either humoral or neural may affect renal and perhaps other arteries. It is interesting to speculate on how much these abnormal responses are present in subsequently hypertensive patients, and how much of a role they play in adverse reactions to contrast material.