Objective: It is to explore the status of heme oxygenase carbon monoxide system in hypertension. Methods: Eight spontaneous hypertensive rats (SHRs) and 8 WKYs (with normal blood pressure) were selected. The HO-1 mRNA expression in aortic smooth muscle cell was measured by RT PCR. Results: HO 1mRNA expression in vascular smooth muscle cell in SHRs is lower than in WKYs. Conclusion: The lower gene expression of HO 1 may be play an important role in the mechanisms of primary hypertension.