This study was performed to investigate whether the long-term feeding of a high vitamin E (VE) . diet has a beneficial effect on the decreased cellular immune functions caused by aging. Male Fisher rats, 12 weeks old, were fed a regular (50mg VE/kg diet) or high VE diet (585mg VE/kg diet) for 12 months. Then, the rats were sacrificed under anesthesia and their cellular immune functions were measured. The proliferation of splenic lymphocytes with PHA or Con A was significantly lower in old rats fed the regular diet as compared to that of young rats (two months old). In contrast, the proliferation of splenic lymphocytes in old rats fed the high VE diet was similar to that of young rats. The in vitro effect off macrophages (Mφ) on the proliferation of splenic lymphocytes from young rats was investigated under Con A stimulation. Although splenic Mφ isolated from old rats fed the regular diet did not have any effect on the proliferation of splenic lymphocytes, Mφ from old rats fed the high VE diet significantly enhanced the proliferation of splenic lym-phocytes. The responsiveness of splenic lymphocytes isolated from each group to the Mφ of young rats under Con A stimulation was not significantly different between the young rats and old rats fed the regular diet. In old rats fed the high VE diet, the responsiveness of splenic lymphocytes to young rat Mφ was significantly higher than that of the young rats or old rats fed the regular diet. Furthermore, the high VE diet induced a significant increase in interleukin 2 (IL2) production from splenocytes in both young rats and old rats following in vitro stimulation with Con A for 48 h. These results suggest that VE has the ability to improve the decreased cellular immune functions caused by aging, and appears to be associated with the enhancement of both Mφ functions and lymphocyte responsiveness.