The effect of dextran sulfate on the survival time and mitochondrial function of adriamycin (ADM)-treated mice was studied. ADM-induced toxicity in mice was reduced by treatment with dextran sulfate (60, 100, 300, and 600 mg/kg, sc). The optimum dextran sulfate dose for protection against ADM-induced toxicity in mice was about 200 mg/kg/day (sc) and 100 mg/kg/day (po). Groups treated with dextran sulfate (300 mg/kg) had significantly improved mitochondrial function as measured by oxygen uptake of state 3 (p less than 0.01), dinitrophenol-altered respiration (p less than 0.01), and respiratory control index level (p less than 0.01). From these observations, it was concluded that ADM-induced toxicity due to reduced mitochondrial function can be ameliorated by the membrane stabilizing effect of dextran sulfate.