The prevalence of metronidazole and clarithromycin resistance of Helicobacter pylori strains under different growth conditions (microaerophilic or anaerobic preincubation) was tested in 56 patients suffering from gastritis and peptic ulcer. vacA subtypes were detected in 46 H. pylori strains and were subsequently compared with the antibiotic resistance pattern. From 56 isolates, 26 proved resistant and 30 sensitive to metronidazole. The patients with peptic ulcer and gastritis were infected with both metronidazole-sensitive and metronidazole-resistant strains. In anaerobic preincubation all the strains were sensitive to metronidazole (MIC < 8 mg/l). All the strains were clarithromycin-sensitive (MIC < 2 mg/l). In the patients with gastritis and peptic ulcer s1 was the predominant vacA subtype. Comparison of vacA subtypes with the diagnoses revealed no correlation; different virulence factors such as vacA subtypes and antibiotic resistance to metronidazole in a microaerophilic milieu proved unrelated.