The increasing awareness of the role of obligate anaerobic bacteria in the aetiology of oral disease has led to an interest in their chemotherapeutic control. Many drugs are capable of eliminating anaerobes but in instances where these bacteria are acting as sole or major pathogens it is desirable to remove these specifically. The nitroimidazole group of drugs is specifically anti-anaerobic in nature and includes metronidazole, nimorazole and tinidazole. This paper reviews the literature on metronidazole. This drug is absorbed well from the gastrointestinal tract and can be detected at bactericidal levels in blood and saliva within 1 h of ingestion. The mode of action of metronidazole is unknown but thought to concern intracellular reduction of the molecule. The drug acts specifically against anaerobes and does not disturb the commensal aerobic flora; resistance very rarely develops. The dosage recommended for use in dentistry would appear to be very safe. Metronidazole has important interactions with alcohol, disulfiram and warfarin and there are contraindications to its use. Metronidazole has been proved to be efficacious in treating: acute ulcerative gingivitis, pericoronitis, certain periapical infections, some cases of osteomyelitis and infected socket. The drug may be of use in cases of chronic progressive periodontitis where anaerobes are implicated as pathogens.