In normal microsome, both NADH-ferricyanide dehydrogenase and NADH-cytochrome c reductase were almost completely solubilized by 0.5% DOC treatment, solubilization patterns of these enzymes being little affected by CCl4 injected treatment. On the other hand, in membranes, solubilizations of dehydrogenase and reductase were less than those in microsomes. Moreover, CCl4 administration lowered the solubility of the dehydrogenase in membranes and increased 3-fold the rate of reductase/dehydrogenase remaining in non-solubilized fractions. Reductase in membranes from CCl4-treated rat liver was found to be more resistant to solubilization by DOC.