BACKGROUND/PURPOSE Total ischemia/reperfusion (I/R) of the small intestine induces cellular apoptosis. In this study, the authors investigated the effects of fetal bovine serum (FBS) on apoptosis and related proapoptotic and antiapoptotic factors in the I/R-injured small intestine of mice. METHODS The mice underwent total I/R of the small intestine and were treated with oral gavages of normal saline or FBS for 3 days, concluding with total ischemia of the small intestine. Samples of the I/R-injured small intestine, representing various predefined time-points post-I/R (immediately before and after 1 hour of total ischemia and at 1, 6, and 24 hours after initiation of reperfusion), were subjected to terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining to study the cellular apoptosis, and Western blot analysis to measure expression of p53, bcl-2 and bax, with caspase-activity assay used to determine the activity of caspase 3. RESULTS For the saline-treated mice, increased cellular apoptosis, suppressed expression of p53 and bcl-2 (with decreased bcl-2 to bax ratio) and increased caspase-3 activity were found for the I/R-injured small intestine. By contrast, FBS treatment suppressed cellular apoptosis, producing up-regulation of p53 and bcl-2 (with increased bcl-2 to bax ratio to 5.4-fold of the saline-treated group) and inhibiting the activity of caspase 3 (P <.05). CONCLUSIONS The results of our study suggest that I/R-induced apoptosis of the mouse small intestine may be related to p53 and bcl-2 suppression (with decreased bcl-2 to bax ratio) and activation of caspase 3 and that such apoptosis seems to be suppressed by FBS treatment.