Aim: To screen 90 clinical isolates of thermophilic Campylobacter species for putative resistance to ampicillin, erythromycin and tetracycline and perform numerical analysis to determine isolate relatedness. Methods and Results: Disc diffusion, E-test MIC and agar dilution methods were performed. Disc diffusion testing showed 87 (97%) isolates appeared resistant to ampicillin at 10 mu g; 14 (16%) resistant to tetracycline at 30 mu g; and three (3.4%) resistant to erythromycin at 15 mu g. E-test MICs showed a range of 0.5 to >256 mg l(-1) for ampicillin; 16 to >256 mg l(-1) for tetracycline; and >256 mg l(-1) for erythromycin. E-test showed 68% correlation (+/-1 log(2) dilution) with agar dilution for ampicillin, 100% for erythromycin and 64% for tetracycline. Disc diffusion testing showed 100% correlation with agar dilution for erythromycin and tetracycline, and 77% for ampicillin. Numerical analyses of restriction endonuclease (RE) fragment profiles suggested a high level of isolate variation. Conclusion: The incidence of resistance of thermophilic Campylobacter spp. to erythromycin and tetracycline is low in south-east Queensland. Significance and Impact of the Study: Disc diffusion susceptibility testing may be used to screen thermophilic Campylobacter spp. for putative resistance to erythromycin and tetracycline. Agar dilution should be used to determine ampicillin susceptibility.