Increased oxidative stress is a common finding in diseases such as diabetes (1). Cumene hydroperoxide is an organic compound commonly used to induce free radical formation in vitro to mimic oxidative stress (2). We examined the effect of this compound on the relaxation induced by a variety of agonists in the rat aorta. Segments of the aorta from Sprague Dawley rats mounted in organ baths were incubated for 30 or 120 minutes in physiological salt solution containing 100 or 300 uM of Cumene hydoperoxide (CHP) before concentration-response curves were constructed for acetylcholine (Ach, endothelium-dependent relaxant), sodium nitroprusside (SNP, non endothelium-dependent nitric oxide donor), Levcromakalim (ATP-sensitive potassium channel opener), Naringenin (large conductance potassium channel opener) and forskolin (activator of adenylyl cyclase-Protein kiase A pathway). Relaxations to all agonists were severely impaired by CHP (100 or 300 µM) following exposure for as little as 30 minutes. The concentration-response curves for Ach, SNP, levcromakalim, Naringenin and forskolin were all significantly (p<0.05, t-test and ANOVA) shifted to the right of respective controls. PD2 for levcromakalim and forskolin were significantly (p<0.05, unpaired t-test and ANOVA) increased, while the Emax for all the agonists except for forkolin were significantly (p<0.05, unpaired t-test and ANOVA) reduced. The results show that CHP non-selectively alters the mechanisms of relaxation of the rat aorta resulting in generalized impairment in responses. This suggests that CHP may not be an ideal agent for induction of oxidative stress intended to target a specific cellular pathway.