Campylobacter spp. are a frequent cause of diarrhoea in man, originating mostly from poultry. It has been suggested that the veterinary use of antibiotics is largely responsible for resistance in human isolates, particularly to quinolones. During a 6 month period from June to December 1998, 677 Campylobacter isolates were obtained from healthy poultry and pigs. Samples were taken at Belgian slaughterhouses. Species identification was performed by biochemical tests, multiplex PCR and SDS-PAGE of whole-cell proteins. The in vitro susceptibility to six antimicrobial drugs was determined by the agar dilution method. Campylobacter jejuni was found more often in poultry than Campylobacter coli (79% C. jejuni versus 21% C. coli). In pigs the situation was reversed (6 versus 94%). Erythromycin resistance was significantly higher (P < 0.05) in C. coli, particularly in C. coli isolated from pigs (67.2%). Alarmingly high rates of resistance to ciprofloxacin were also noted, particularly for C. coli from broilers (62.1%). The latter indicates that resistance of Campylobacter in humans could derive from animals.