Twenty-three antimicrobial agents, including 4 new broadspectrum beta-lactam antibiotics were tested against 50 clinical isolates of Campylobacter jejuni. The activity of metabolites of metronidazole and tinidazole was also tested. Minimum inhibitory concentrations (MIC) were determined by agar dilution. beta-lactamase production was detected by a chromogenic cephalosporin method. All strains were susceptible to erythromycin, clindamycin, chloramphenicol, furazolidone, aminoglycosides (including gentamicin), cefotaxime and NF-thienamycin. All isolates were resistant to penicillin, cephalothin, cefoperazone, vancomycin, rifampicin and trimethoprim; beta-lactamase was detected in 2% of isolates. Some strains were resistant and others sensitive to the other drugs tested, which included ampicillin, moxalactum tetracycline, metronidazole and tinidazole. The 'hydroxy' metabolites of metronidazole and tinidazole were more active than the parent compounds.