In this podcast, I speak to Martin Blaser, Frederick H. King Professor of Internal Medicine and Chairman of the Department of Medicine and Professor of Microbiology at the New York School of Medicine. Blaser studies Helicobacter pylori, bacteria that live in the stomachs of billions of people. Blaser has shown that H. pylori has a strange double life inside of us. On the one hand, it can cause ulcers and gastric cancer. On the other hand, it can protect us from diseases of the esophagus, allergies, asthma, and perhaps even obesity. We're now eradicating H. pylori with antibiotics and other luxuries of modern life; Blaser thinks we ought to bring it back--but keep it on a tight leash.