Abstract: A method for the simultaneous determination of Matrine and Oxymatrine in the same biological materials and the metabolic fate of the latter compound are described.There is a wide variation between the distribution and excretion of Oxymatrine administered to rats by different routes. After im injection of Oxymatrine, the parent drug concentration was found to be high in the tissue, bile and urine. However, when Oxymatrine was given orally, Matrine concentration was higher than that of Oxymatrine in all tissues. This indicates that Oxymatrine may be converted to Matfine in the G-Ⅰ tract. After absorption, Matrine was distributed to the tissues and excreted in the urine. After iv injection, Oxymatrine rapidly disappeared from plasma.These results showed that Matrine is probably the pharmacologically active substance in the treatment of asthma.Institute of Materia Medica, Chinese Academy of Medical Sciences, BeijingDepartment of Pharmacology, Quiyang Medical College.