Semi-purified diets containing 30 ppm or 500 ppm dl-?-tocopherol (VE) were fed for 8 weeks to young (3 months) and old (18 months) Swiss mice. The blastogenic response of splenocytes as well as serum VE and lipid peroxides (LPO) in livers were measued. The results showed that the old mice fed 500 ppm VE had a significantly higher serum VE level and blastogenic response of splenocytes to Con A and LPS than those fed 30 ppm VE (p