The aim of the present study was to clarify the issue of lipid peroxidation operating in visual system structures and sciatic nerve of the rat as a contributing factor to senescence. In 4-, 14- and 28-month-old male rats, the amount of endogenous malondialdehyde, conjugated dienes and extractable phospholipids were all taken as indices of lipid peroxidation. In addition, the total free and released enzyme activities of four lysosomal hydrolases were evaluated. The susceptibility of all these parameters to in vitro iron-induced peroxidation was also taken as an age-related indicator of the endogenous peroxidative potential of the nervous tissues examined. Our data show that the content of malondialdehyde and phospholipids did not change in an age-related fashion. Furthermore, the susceptibility of rat visual system structures to lipid peroxidation, together with the release of lysosomal enzymes were unchanged as a function of aging. The results do not lend support to the hypothesis that an increase in overall lipid peroxidation is peculiar to the aging phenomenon of the central nervous system areas which delimit the rat visual pathway.