The in vitro antioxidative activity of benzylideneascorbate (SBA) and the in vivo effect on adriamycin (ADR)-induced cardiotoxicity in a mouse model were investigated The radical-scavenging activity of SEA was assayed in terms of reduction of chemiluminescence induced by O-2-, generated in xanthine/xanthine oxidase and macrophage/phorbol myristate acetate reaction systems. SEA showed a strong antioxidative activity (IC50 = 3 to 4 mu M) in both assay systems, though its activity was weaker than that of ascorbic acid (Asc). In the assay of the antioxidative activity against auto-oxidation of linolenic acid, SEA was stable and retained its potency for a long period of time in comparison with Asc, 6-palmitoylascorbic acid (6-P-Asc) and cysteamine (CysNH2). Electron spin resonance examination indicated that SEA strongly scavenged both superoxide anion and hydroxy radical. The in vivo protective effect of SEA against ADR-induced cardiotoxicity, in which active oxygen radicals play a role, was examined. The serum creatine phophokinase activity, a parameter of cardiotoxicity, was remarkably increased from the 3rd day until the 4th day after ADR treatment. This elevation was significantly suppressed by SEA treatment, whereas Asc, 6-P-Asc and CysNH2 were ineffective. SEA could have clinical potential for the treatment of diabetes and other disorders in which active oxygen species play a pathogenic role.