Abstract Our aim was to study the effect of pure mastic gum on Helicobacter pylori (H. pylori) eradication in patients suffering from an H. pylori infection Fifty two patients were randomized to receive either 350 mg three times a day (tid) of pure mastic gum for 14 days (Group A), or 1,05 g tid of pure mastic gum (Group B) for 14 days, or pantoprazole 20 mg twice a day (bd) plus pure mastic gum 350 mg tid for 14 days (Group C) or pantoprazole 20 mg bd plus amoxicillin 1 g bd plus clarithromycin 500 mg bd for 10 days (Group D). All patients harboured H. pylori before entering the study and that was confirmed by a 13C urea breath test (UBT). H. pylori eradication was tested by a UBT 5 weeks after completion of the eradication regime. Eradication of H. pylori was confirmed in 4/13 patients in Group A and in 5/13 in Grour B. No patient in Group C achieved eradication whereas 10/13 patients in Group D had a negative UBT. There were no statistically significant differences in mean UBT values in Groups A, B, C although there was a trend in Group A (p=0.08) and in Group B (p=0.064). The difference was significant in Group D (p=0.01). All patients tolerated mastic gum well and no serious adverse events were reported. Mastic gum has bactericidal activity on H. pylori in vivo.