Liver peroxisomal beta-oxidation activity on stearate, oleate, linoleate and alpha-linolenate was investigated as a function of age in two mouse strains. Each fatty acid showed a similar beta-oxidation activity pattern with age characterized by a rapid increase (200%) from day 2 to 20 followed by a dramatic weaning-related decrease (70%) from day 20 to 22. There was a new increase (260%) from day 22 to 75, then a plateau up to day 300 days, and finally an age-related decrease (70%) from day 300 to 540. Oleic, linoleic and alpha-linolenic acids were respectively 5-, 7.5- and 9-fold more degraded than stearic acid. Catalase specific activity showed the same age-related pattern as fatty acid beta-oxidation. Both mouse strains showed the age-related decreases. The longer-lived strain exhibited higher activity for both peroxisomal beta-oxidation and catalase and the rate of decrease of these two activities during aging was the same for both strains. The catalase/alpha-linolenic acid beta-oxidation ratio was constant during adulthood and aging. These results suggest that peroxisomal beta-oxidation and catalase activities are closely related throughout and implications for long-chain and very long-chain fatty acid metabolism, maintenance of membrane fatty acid composition and anti-oxidant status during aging are discussed.