The aim of our study was to investigate the changes in the early stages (at weeks 2 and 4) of experimental acute renal failure after short-time ischemia-reperfusion (I/R) compared with the impact of Losartan. Twenty male Wistar rats were divided into three groups: sham-operated rats (2 weeks), I/R groups (2 and 4 weeks); I/R and Losartan-treated groups (2 and 4 weeks). I/R was produced in adult rats by clamping the left kidney renal artery and renal vein for 40 min. The angiotensin II receptor antagonist Losartan was added to the drinking water (40 mg/l), and treatment was started on the first day after the I/R. Body weight, systolic blood pressure (SBP) and 24 h urine amount was measured every week. Urine amount and SBP was higher in I/R groups compared to sham-operated rats. Early stage acute renal disease was characterized by focal segmental glomerulosclerosis (FSGS) and interstitial fibrosis (IF) at weeks 2 and 4 after I/R. In the Losartan group, 2 weeks after the surgery, FSGS, IF and mesangial cell proliferation was decreased, but at week 4 these parameters showed a tendency to increase. Marked changes take place in tubular epithelial cells, especially in I/R groups. Angiotensin II receptor blocker AT1RA Losartan in the small dose (40 mg/l) had no effect on hypertension and urine excretion in the experimental I/R model. A pilot study revealed that tubular basement membrane thickness is markedly increased after I/R.