The reactive oxygen radicals produced from human polymorphonuclear leukocytes (PMN) stimulated with PMA (phorbol myristate acetate), hydroxyl radicals generated by a Fenton reaction, and superoxide anion radicals produced by irradiating solutions of riboflavin in the presence of EDTA have been taken as the models for production of oxygen radicals. With the use of the electron spin resonance spin trapping method, the scavenging effects of schizandrol A (solA) (5 x 10(-4) M) and schizandrin B (sinB) (5 x 10(-4) M) have been studied and compared with the effects of vitamin E (5 x 10(-4) M) and vitamin C (5 x 10(-4) M). It has been found that in cell system the scavenging effects of sinB and solA, as judged by ESR spin trappings, on hydrpxyl radicals (.OH) are greater than vitamin E and vitamin C and the scavenging effects on superoxide anion (O2) are greater than vitamin E but lower than vitamin C. With respect to the Fenton reaction, sinB has the strogest scavenging effect on .OH (77%) and solA has strong scavenging effect on .OH (63%), both of them larger than that of vitamin E (35%) and vitamin C (56%). In the riboflavin/EDTA system, the scavenging effect of sinB (46%) is smaller than that of vitamin C (96%) but larger than that of vitamin E (23%); the scavenging effect of solA is not obvious (14%). With the use of spin probe oximetry, the oxygen consumption during the respiratory burst of stimulated PMN has been measured when exposed to schizandrins. The experiment results demonstrated that they do not affect the activity of production of active oxygen radicals in the respiratory burst of PMN stimulated with PMA.