The search for methods to control physiological levels of carbon monoxide (CO), a vasoactive molecule, and bilibrubin, an antioxidant, have improved our understanding of the protective role of heme oxygenase (HO) against oxidative injury. HO activity can assist other antioxidant systems in diminishing the overall production of reactive oxygen species, thus contributing to cellular resistance to such injury. Overexpression of HO gene by targeted gene transfer has become a powerful tool for studying the role of this human enzyme. Successful and functional HO gene transfer requires two essential elements. First, the HO gene must be delivered into a safe vector, such as the adenoviral, retroviral and leptosome based vectors that are currently being used in clinical trials. The use of non-viral vectors has also been described. Second, with the exception of HO gene delivery to ocular or cardiovascular tissue via catheter-based interventions, HO gene delivery must be site and organ specific. Site-specific delivery of HO-1 to renal structures in SHR, specifically mTAL, using Na+-K+ Cl - cotransporter (NKCC2 promoter), has been shown to normalize blood pressure and provide protection to mTAL against oxidative injury, respectively. Human HO-1 gene transfer into endothelial cells has been shown to attenuate Ang II- TNF- and hememediated DNA damage. Furthermore, delivery of human HO-1 into SHR has been shown to enhance somatic body growth and cell proliferation. The ability to transfect human HO gene and to demonstrate its expression may offer a new therapeutic strategy for treating pathological conditions, such as hypertension, trauma and hemorrhage.