To investigate the cytotoxicity of Radix isatidis samples from heat processing in this study. Madin- Darby Canine Kidney cell has been well subjected to determination of influenza virus and studies on antivirus drugs. The cytotocity of fresh root of Isatis indigotica,Radix Isatidis and Radix Isatidis decoction were determined to evaluate the survival of the cells by MTT( methyl- thiazolyl-tetrazolium) assay. The toxic concentrations for 50% of fresh root of Isatis indigotica,radix isatidis and radix isatidi...