This study focused on the frequency of Campylobacter jejuni and Campylobacter coli strains resistant to norfloxacin. Included were 1659 consecutive stool specimens isolated between 1992 and 1995, from as many Swedish patients with diarrhoea. The patients were divided with regard to place of infection and age. All strains were tested for susceptibility to norfloxacin by means of disc diffusion test on blood-agar plates. Norfloxacin-resistant strains (n = 310) were furthermore tested for resistance to doxycycline and erythromycin. The Etest was used for determination of MIC values of doxycyclin, erythromycin and norfloxacin of 81 of the strains. C. jejuni and C. coli isolations resistant to norfloxacin were significantly more frequent among patients infected abroad, especially in Spain and Thailand, compared with those infected in Sweden, adults more often than children. The number of resistant strains showed a yearly increase, and the difference between children and adults was equalized in 1995. The MIC50 and MIC90 values for doxycycline and erythromycin have increased markedly through the 4 years studied. This study shows that norfloxacin, because of increased resistance, may have limited utility for treatment of gastrointestinal infections caused by C. jejuni and C. coli.