The effects of chronic dietary protein restriction on ischemic renal failure were evaluated in rats subjected to 90 min of bilateral renal clamping. The rats were kept on either 20% casein (regular) diet or casein-free dprotein-free) diet 10 days before and 21 days after renal injury. Rats on regular protein diet showed higher levels of BUN and serum creatinine and had a lower inulin clearance (pl/minlIOO g BW) than animals on protein-free diet (289 f 34 vs 582 f 103, p<0.05) 2 days after ischemia. However, the inulin clearance measured 21 days following ischemia was signijicantly higher in rats on regular diet (1 468 f 181) than those maintained on protein-free diet after ischemia (560 f 167). when unilateral 90 min ischemia was pedormed in rats on regular diet, the postischemic kidneys showed an incomplete recovery of the inulin clearance (226 35) compared to the contralateral kidney (900 f 116), 21 days afer ischemia; whereas in rats on a protein-free diet the in- ulin clearance averaged I 0 6 f 17 in the postischemic kidney and 345 f 41 in the right kidney, when left renal ischemia and contralateral nephrectomy were pedomd, the inulin clearance was 1149 f 74 in rats on regular diet and 534 f 60 in rats on protein-pee diet, 21 days following renal insult. These results suggest that protein restriction can play a protective role against renal ischemia in an initial phase, but it limits the lute recoveryfrom ischemia. The presence of a normal contralateral kidney inhibits the functional recovery of the postischemic kidney and a contralateral nephrectomy produces a compensatory functional hypertrophy of the postischemic kidney, even in rats on a protein-free diet.