The Shandong Intervention Trial was a factorial, double-blind, placebo-controlled trial to determine whether any of 3 interventions, alone or in combination, could reduce the prevalence of precancerous gastric lesions in Linqu County, Shandong Province, China, a region with high gastric cancer mortality rates and a prevalence in adults of Helicobacter pylori of approximately 67%. The 3 interventions were one-time treatment with amoxicillin and omeprazole for Helicobacter pylori infection, and long-term administration of a garlic supplement (aged garlic extract and steam-distilled garlic oil) and a vitamin supplement (vitamins E and C and selenium). This paper describes the design and initial findings on treatment compliance, completeness of follow-up data, and eradication of Helicobacter pylori.