Resistance rates to three antimicrobials (ciprofloxacin, erythromycin and nalidixic acid) in Campylobacter isolated from organically- and intensively-reared chickens purchased from supermarkets and butcher's shops in London were determined. Significant differences in the minimum inhibitory concentrations (MICs) of nalidixic acid were found, with the highest values in unpackaged intensively-reared chickens and the lowest values in organically-reared chickens. Using pre-set breakpoints, all isolates from all groups of chickens were identified as resistant to erythromycin and nalidixic acid. All isolates from the organically-reared group were susceptible to ciprofloxacin. Of the supermarket intensively-reared chickens, 8.7% harboured resistant isolates, all on the external parts, indicating post-slaughtering contamination. The highest percentage (26.7%) was in chickens from butcher shops, mostly in the chicken cavities, suggesting a link to treatment on the farm.