No accurate, inexpensive, and noninvasive test for gastric cancer screening is currently available. Our recent study identified alpha1-antitrypsin as a potential biomarker of gastric cancer in gastric juice. The aim of this study was to develop a novel noninvasive modality for detecting gastric cancer by measurement of alpha1-antitrypsin concentration in gastric juice. The work consisted of two parts: (a) investigating the differences in gastric juice alpha1-antitrypsin concentrations between gastric cancer patients and controls, and (b) screening gastric cancer using string test to obtain gastric juice followed by immunoassay for alpha1-antitrypsin concentration. The data showed that gastric juice alpha1-antitrypsin concentration was markedly higher in gastric cancer patients than in healthy subjects, gastric ulcer patients, and duodenal ulcer patients (all P < 0.001). The area under the receiver operating characteristic curve for identifying gastric cancer cases was 0.96 (95% confidence interval, 0.93-0.99; P < 0.001). The sensitivity and specificity of gastric juice alpha1-antitrypsin concentration were 96% and 92%, respectively. Gastric juice alpha1-antitrypsin assay through string test was validated in 93 consecutive patients for gastric cancer screening. The sensitivity and specificity of gastric juice alpha1-antitrypsin string test at 85% accuracy were 74% and 88%, respectively. The area under the receiver operating characteristic curve for identifying gastric cancer was 0.84. In conclusion, gastric juice alpha1-antitrypsin concentration in gastric cancer patients markedly exceeds those in healthy subjects and patients with benign gastrointestinal diseases. A noninvasive alpha1-antitrypsin string test may serve as a new screening tool for identifying gastric cancer patients. Cancer Epidemiol Biomarkers Prev; 19(2); OF1-7.