This study investigated the effects of renin- angiotensin system ( RAS) blockade on stress- induced changes of serum vascular endothelial growth factor ( VEGF) and nitric oxide ( NO) in mice. Chronic stress increased the serum NO levels significantly compared to control group ( p =.0172). Valsartan, an angiotensin II receptor antagonist, alone, did not make significant difference versus control group. In chronic stress + valsartan group, serum NO levels decreased nonsignificantly compared to chronic stress group. There was a nonsignificant increase in serum VEGF levels after chronic stress. Valsartan alone or with chronic stress did not significantly affect the serum VEGF levels. In conclusion, there was no correlation between NO and VEGF changes during the stress response. In this respect, there may be other mechanisms to explain the stress- induced NO increase.