Aging in both humans and rodent models is typically associated with an increase in fat mass while endurance exercise reduces total fat mass. We hypothesize that aging in Fischer-344 rats will cause adaptations in adipose tissue that promote increased fat storage, while endurance exercise training will cause adipose tissue to resist fat deposition. Earlier work identified 19 genes whose expression in adipose tissue appeared to be affected by exercise training in aged rats. This work focuses on one of those genes, DNA binding inhibitor-1 (ID1), which has been shown by others to regulate adipocyte proliferation and differentiation. The goal of this work is to use real-time polymerase chain reaction to verify that exercise training reduces the expression of this gene in aged rats. In addition, we are also determining if expression of this gene is affected by aging, and if the effect of exercise training on ID1 gene expression is different between 15 month old, and 27 month old rats.