5,8-dihydroxy-1,4-dihydro-1,4-methanonaphthalene (DDMN), a substituted phenol, is synthesized by the reduction of a cyclic dione, 1,4,4a,8a-tetrahydroendo-1,4-methano-naphtha-5,8-dione (THMND). The pulse radiolysis technique has been employed to understand the nature of transient species formed by the reaction of radiolytic species of water radiolysis with DDMN. • OH radicals were observed to react with DDMN with a bimolecular rate constant of 1.5 9 10 10 dm 3 mol -1 s -1 . The inhibition of radiation-induced lipid-peroxidation by DDMN was studied in rat liver microsomes by assessing the formation of thiobarbituric acid reactive substances (TBARS). It was found to be strongly inhibitory. The results suggest that DDMN has very good antioxidant activity and may possibly emerge as a good radio-protector.