Both angiotensin II (AII) and atrial natriuretic polypeptide (ANP) are related to the function of blood vessels, but differ in their actions. The authors observed the effect of Salvia miltiorrhiza Co. (SMC) on the activities of AII and ANP in rabbits by radioimmunoassay. It was found that the concentration of AII and ANP in plasma were significantly lower (P less than 0.05), and slightly lower in brain and atrial (P greater than 0.05) in SMC group than in control group. It indicated that the effect of SMC on blood vessels is related to changes of AII and ANP, and that the difference of peptide changes in brain and plasma might be due to the blood-brain barrier.