Plant extracts from Kampo medicines TJ-9 (A), TJ-15 (B), TJ-23 (C), TJ-114 (D) and TJ-96 (E) inhibited peroxidation of low-density lipoprotein (LDL) in vitro and peroxidation of multilamellar liposomes formed by total lipids isolated fro the rat brain. The order of relative efficacy of the extracts in both experiments was as follows: C < D equal to or greater than A < B. Using EPR spectroscopy, the Kampo extracts were found to be oxidated by means of PbO2 and to become relatively stable radicals, which shows that they possess electro-donor properties. A relationship between their ability to inhibit peroxidation of LDL and liposomes and their ability to become a radical was found. The Kampo medicines which produced more radicals inhibited peroxidation of LDL and liposomes more effectively. By means of EPR spectroscopy, Kampo B was found to reduce the vitamin E radical. The results contribute to the understanding of the positive effects of Kampo extracts in the diseases in which a negative influence of free radicals is assumed.