Recent findings have shown that microsomal membrane lipid peroxidation generates a variety of reactive aldehydic products. The interaction of lipid peroxidation products with hepatic aldehyde dehydrogenases (ALDH) was studied using rat liver subcellular fractions. The well-documented membrane peroxidation product malondialdehyde (MDA) was studied to determine if ALDH isozymes play a role in metabolism of this aldehyde. The cytosolic and mitochondrial hepatic subcellular fractions were found to contain ALDH isozymes capable of oxidizing MDA. The kinetic properties of a cytosolic ALDH (Km of approximately 16 microM) suggest that this enzyme may be involved in the metabolism of MDA in vivo. Both the cytosolic and mitochondrial fractions also contained an ALDH isozyme with Km values in the millimolar range. Addition of the cytosolic fraction of rat liver produced a significant decrease in the accumulation of MDA during CCl4-induced microsomal membrane lipid peroxidation but did not protect cytochrome P-450 from destruction. The mitochondrial low Km ALDH isozyme was found to be a target enzyme for inhibition during in vitro microsomal lipid peroxidation. These studies show that a select ALDH isozyme is sensitive to inhibition during membrane lipid peroxidation whereas other isozymes may be involved in the metabolism of aldehydic peroxidation products.