Amphotericin B systemically infused into anesthetized rats at the rate of 0.4 mg/kg body weight over 20 min reproducibly induced renal vasoconstriction and renal cortical hypoxemia. By contrast, when infused with albumin (3 g/dl), amphotericin B did not reduce renal blood flow and did not affect renal cortical oxygenation. In vitro, hemolysis induced by amphotericin was also markedly reduced in the presence of albumin. Albumin did not appear to reduce the antibiotic effect of amphotericin in vitro. It was concluded that amphotericin B toxicity may be considerably reduced if administered in an albumin vehicle.