Dextran 40 is largely used in clinical medicine as a plasma substitute because of its beneficial effects on the microcirculation and antithrombogenic properties. An unusual adverse reaction of dextran administration is oligoanuric acute renal failure. We report two cases of anuric ARF induced by dextran 40. Diuresis and renal function were quickly resumed after plasma-pheresis treatment. Renal biopsy revealed normal kidneys except for swelling and vacuolation of renal tubules suggestive of osmotic nephrosis.