The in vitro antimicrobial activity against H. pylori and clinical efficacy of various antibiotics and antiulcer drugs are summarized in this study. H. pylori highly sensitive to most of the beta-lactams and macrolides. Especially, amoxicillin and clarithromycin have satisfactory in vitro activity against H. pylori. The anti-ulcer drugs, sofalcon and plaunotol, used in Japan as mucosal protective agents, also have a weak activity against H. pylori with MIC50 12.5 micrograms/ml and MIC90, 50-100 micrograms/ml, while H2-receptor antagonists do not have in vitro activity. Efficacy of antibiotics as monotherapy for eradicating H. pylori is rather poor. The best results with monotherapy are obtained with clarithromycin and amoxicillin. Omeprazole monotherapy suppresses H. pylori infection but does not eradicate H. pylori. Combined therapy with omeprazole and amoxicillin have strong synergistic effects on the eradication of H. pylori (68.8%). Newly developed proton pump inhibitors, such as lansoprazole, E-3810 and their derivatives, showed strong in vitro activity against H. pylori suggesting that these drugs may be useful for the treatment of H. pylori infection.