Gastroduodenal ulcers are strongly associated with Helicobacter pylori (HP) infection. Successful eradication drastically diminishes ulcer recurrence. Most of the eradication schemes include metronidazole (Flagyl). The present study was designed to establish the metronidazole resistance rate in Switzerland. Antral biopsies were taken in 153 patients with suspected ulcers (115 men, 38 women, mean age 46 +/- 16 [SD] years) during upper endoscopy for bacteriological testing. Metronidazole resistance (> 8 micrograms/ml) was found in 47/153 (31%) of the isolates. Resistance was found in no case to amoxicillin (Clamoxyl) (0/104 = 0%) and only in 3% (2/66) to clarithromycin (Klazid). Metronidazole resistance of HP in a third of the isolates studied is comparable to numbers found in other European countries. These findings raise the question whether eradication schemes including metronidazole without prior sensitivity testing are justified. Amoxicillin and clarithromycin appear to be valid alternatives.