The susceptibilities of 115 campylobacters, belonging to five species, to metronidazole, its principal oxidative metabolites and tinidazole were determined by an agar dilution method. The activities of metronidazole and tinidazole were comparable. The hydroxy metabolite was more active than the parent drug against most species, particularly Campylobacter jejuni and Campylobacter pyloridis. Although the acid derivative was less active against C. jejuni and Campylobacter coli, it demonstrated an equivalent degree of activity to metronidazole against the remaining species. Inter-species differences existed with respect to the susceptibility of campylobacters and selected nitroimidazole antimicrobials.