Enzymatically isolated hepatocytes were utilized to evaluate levels of lipid peroxidation in young (3 months), adult (12 months) and aged (25 months) Fisher-344 female rats. Lipid peroxidation was measured by assaying levels of malonaldehyde, a by-product of the peroxidation reaction. Young, adult and aged animals were fed a liquid antioxidant-free diet for 21 days prior to the hepatocyte isolation. Cells isolated from young rats demonstrated the highest levels of lipid peroxidation (microgram of malonaldehyde/10(6) cells). This increase may be a result of the isolation procedure or of metabolic differences found in younger animals. When hepatocytes from aged animals on the antioxidant-free diet were incubated in the presence of lipid peroxidation inducers, such as cumene hydroperoxide or NADPH, significant elevations in lipid peroxidation over comparable adult values were observed. Aged hepatocytes appear to be more susceptible to the peroxidation process than adult hepatocytes, possibly due to defective peroxidation defenses.