Background People have more and more concerned about allitridum as studies have shown that taking more raw garlic associated with a lower risk for cancers of the alimentary system In the present study, we tried to examine whether a large dose of allitridum and a microdose of selenium prevent gastric cancer Methods A double-blind intervention study was performed on the participants aged (35-74) years, who had matched at least one of the following criteria: (1) a medical history of stomach disorder, (2) a family history of tumour, or (3) smoking and/or alcohol consumption A total of 2526 and 2507 persons were randomly enrolled into intervention group and control group respectively from 288 natural villages of seven communities in Qixia County, Shandong Province, China Each person of the intervention group orally took 200 mg synthetic allitridum every day and 100 μg selenium every other day for one month of each year during November 1989 to December 1991. At the same time, people in control group were given 2 placebo capsules containing corn oid with the identical appearance to that in the intervention group Results For all subjects the large dose of allitridum was accepted and no harmful side effects were found during the study In the first follow-up five years (1992-1997) after stopping the intervention, the morbidity rates of malignant tumours in the intervention group declined by 22%, in contrast to the control group, declined by 47 3% After adjusting for age, gender, and other potential confounders, relative risks (RRs) for all tumours and gastric cancer of the whole population were 0 67 (95%CL: 0 43-1 03) and 0 48 (95%CL: 0 21-1 06), respectively, and for male group they were 0 51 (95%CL: 0 30-0 85) and 0 36 (95%CL: 0 14-0 92), respectively. No signigicantly protective effect was found for the female subgroup DConclusion The present study proves that large doses of allitridum and microdorse of selenium may effectively prevent gastric cancer ,especially in men Background People have more and more concerned about allitridum as studies have shown that taking more raw garlic associated with a lower risk for cancers of the alimentary system In the present study, we tried to examine a large dose of allitridum and a microdose of selenium prevent gastric cancer Methods A double-blind intervention study was performed on the participants aged (35-74) years, who had matched at least one of the following criteria: (1) a medical history of stomach disorder, (2) a family history of tumour, or (3) smoking and / or alcohol consumption A total of 2526 and 2507 persons were randomly enrolled into intervention group and control group respectively from 288 natural villages of seven communities in Qixia County, Shandong Province, China Each person of the intervention group orally took 200 mg synthetic allitridum every day and 100 μg selenium every other day for one month of each year during November 1989 to December 1991. At the same time, p eople in control group were given 2 placebo capsules containing corn oid with the identical appearance to that in the intervention group Results For all subjects the large dose of allitridum was accepted and no harmful side effects were found during the study In the first follow-up five years (1992-1997) after stopping the intervention, the morbidity rates of malignant tumours in the intervention group declined by 22%, in contrast to the control group, declined by 47 3% After adjusting for age, gender, and other potential confounders, relative risks (RRs) for all tumors and gastric cancer of the whole population were 0 67 (95% CL: 0 43-1 03) and 0 48 (95% CL: 0 21-1 06), respectively, and for male group they were 0 51 (95% CL: 0 30-0 85) and 0 36 (95% CL: 0 14-0 92), respectively. No sign of protective effect was found for female subgroup DConclusion The present study proves that large doses of allitridum and microdorse of selenium may effectively preve nt gastric cancer, especially in men