The project will develop a simple test for noninvasive diagnosis of active Helicobacter pylori infection in the stomach based on measuring ammonia in patients' breath. A novel highly sensitive optical technique will be used to measure breath ammonia, leading to an inexpensive diagnostic procedure that can be conducted in any general practitioner's office. An improved method of detecting gastric H. pylori is of clinical significance because the organism is the cause of most peptic ulcers and is associated with other gastrointestinal diseases including cancers. The new breath ammonia sensing method will be useful for diagnosis of infected patients, as well as for follow-up determinations of infectious status after therapy. Phase I results demonstrated 100 percent agreement with conventional 14C-labeled breath tests The research will optimize the clinical instrumentation, expand the scope of the Phase I clinical trial to a larger, more diverse patient set, and study test parameters that maximize the clinical diagnostic value of the test. This work will redisign the sensor and instrument as a logical and practical step to final product commercialization. Subsequent pre-market testing for commercialization will implement those instrument and test procedure and confirm their clinical efficacy.