Abstract: A method using thin layer chromatography and dual wavelength. TLC scanner for isolation and quantitative determinination of cryptotanshinone in biological specimens was described. After oral administration of cryptotanshinone to mice, the half life of the drug in the gastrointestinal tract was found to be 3 1/3 hrs. High drug levels were found in the liver, lung, brain and heart 2 hrs after oral administration of cryptotanshinone. The drug levels in the spleen, plasma and kidney were very low. After intravenous injection, the highest drug level was found to be in the brain. In rats only 0.34% of the dose was recovered in the 48-hr urine as unchanged drug after a single oral dose. It is likely that a great part of the drug was metabolized in the body.In rats given an oral dose of cryptotanshinone, seven metabolites were isolated from urine and bile and identified. It was shown that metabolite NO. 6 was unchanged drug, NO. 7 was tanshinone Ⅱ-A, NO. 4 and NO. 5 were hydroxyl forms of tanshinone Ⅱ-A, while NO. 1 was considered to be a glutamic acid conjugate of tanshinone Ⅱ-A. NO. 2, 3, 5 and 6 were shown to have bacteriostatic activity against Staphylococcus aureus (in vitro). The antimicrobial action of NO.6 (unchanged drug) was much stronger than that of the others. Therefore, the unchanged drug was probably the main pharmacologically active form in the body.