...Further development of potent antimicrobial drugs is expected to improve the therapeutic and preventive effects against pathogenesis by H. pylori. Zaidi et al.  have isolated bactericidal constituents from the plant named Mallotus philippinenesis that are effective against clarithromycin-and metronidazole-resistant strains of Japanese and Pakistani H. pylori. On the other hand, mastic gum, which is a resin secreted from the stem of Pistacialentiscus, was found to be effective against H. pylori . In our present study, we examined which component of the essential oil prepared from mastic gum could inhibit the growth of H. pylori. The bactericidal activity of the mastic components will be discussed in association with their drug resistance reversal effects.