We have shown previously that theophylline increases both renal plasma flow (RPF) and glomerular filtration rate (GFR) during the initiation phase of post-ischemic acute renal failure (ARF) in rats. The purpose of the present experiments was to determine the effects of theophylline during the maintenance phase of ARF, five days after initiation. Clearance techniques were used to measure renal function in a control group of pentobarbital anesthetized rats (group C) and in three experimental groups, five days after subjecting the left kidney to a thirty-minute period of complete ischemia. Group SS received saline during both the ischemic episode and the clearance measurements; group ST received saline during ischemia and theophylline, acutely, during the clearance measurements; group TS received theophylline during ischemia and saline during the clearance measurements. In comparison with the values for the control group (group C), RPF and GFR of the post-ischemic left kidneys of group SS were approximately half normal. In groups ST and TS, RPF and GFR of the left kidneys were higher than in group SS. Collectively, these results demonstrate that pretreatment with theophylline during the initiation phase of ischemia-induced ARF leads to increased RPF and GFR during the maintenance phase, and that acute theophylline treatment during the maintenance phase acutely increases RPF and GFR. Since increases in GFR were associated with increases in RPF, and since theophylline is an adenosine receptor antagonist, these results are consistent with the hypothesis that adenosine-mediated hemodynamic changes play a pathogenic role in ischemia-induced ARF in rats.