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Between February 2000 and October 2001, cloacal swabs were collected from 387 broiler chicken flocks in Northern Ireland. Campylobacter isolates from the 262 positive flocks were tested with common antimicrobial agents using a disc diffusion method and by Etests. Resistance to erythromycin, gentamicin and chloramphenicol was <1%, whereas for ampicillin, nalidixic acid and tetracycline, resistance was 33%, 10% and 13%, respectively. Ciprofloxacin resistance was 3%, one of the lowest in recent reports from studies on human or poultry isolates. Sequence data of the quinolone resistance-determining region of the gyrA gene showed a mutation leading to Thr-86 to Ile substitution among highly resistant ciprofloxacin isolates. Only 0.8% of the isolates studied were resistant to four or more antibiotics.