Objective: To observe the effects of Salvia miltiorrhizae composi ta (SMC) on blood gas variations of nitroglycerin (NTG) controlled hypotension. Methods: Sixteen patients who were arranged to under go operation under general anesthesia in controlled hypotension condition were randomly divided into the control group (n=8) and the SMC group ( n=8). NTG was used to create controlled hypotension in both groups and blood pressure decreased by about 30% compared with the control values. Patients in the SMC group were administered intravenously with SMC (16 ml) before the utilization of NTG. Results: Sign ificant PaO 2 decrease and Pa-etCO 2 increase were observed in the control group during the controlled hypotension period. However, blood gas values in the SMC group did not obviously change. Conclusion: SMC can prevent the si de-effects of NTG on blood gas.