Isolated human erythrocyte membrane and platelet were used to study the antioxidative and anti-aggregative effects of three diallyl sulphides (diallyl sulphide, DAS; diallyl disulphide, DADS; diallyl trisulphide, DAT) against glucose-induced oxidation and adenosine 5'-diphosphate (ADP)-induced platelet aggregation. Three sulphide agents showed dose-dependent antioxidative protection against glucose-induced erythrocyte membrane oxidation (p<.05), and these agents at 10 microM significantly increased the retention of alpha-tocopherol in erythrocyte membrane (p<.05), in which DAT was the most effective agent (p<.05). Three sulphide agents significantly inhibited 30 and 50 mM of glucose-induced platelet oxidation (p<.05). The anti-aggregative activity of each sulphide agent was dose dependent (p<.05), in which DAT showed the greatest inhibitory effect on platelet aggregation than DADS, followed by DAS (p<.05). After ADP stimulation, the malondialdehyde (MDA) formation in platelets treated with sulphide agents was significantly less (p<.05), in which DADS and DAT showed similar antioxidative activities (p>.05). These results suggested that DADS and DAT could be considered as strong antioxidative and antithrombotic agents to prevent or control oxidative damage and platelet hyperactivity.