Hepatitis B virus (HBV) is transmitted by infected blood and possibly saliva; faecal-oral transmission is also possible. Infected material is transmitted mostly by the parenteral route. Hence, the transmission of HBV in the dental surgery should be prevented by the routine exercise of good clinical hygiene. As part of patient assessment information on recent hepatitis should be sought. Patients may carry HBV and be infectious from 1 to 4 months after contracting the disease. During this period the surface antigen (HBsAg) can be detected in blood. Symptoms generally appear from 2 to 4 months after infection. High risk groups in the community should be recognized. In communities where the disease is widespread this may include most of the population. Elective dental treatment for patients likely to be infectious should be postponed until the infectious stage has passed; this can be confirmed by showing the absence of HBsAg in blood. A high standard of clinical hygiene, including the routine use of disposable needles for injections, single dose containers for drugs to be injected, sterilized instruments and personal cleanliness before and after treating patients, is essential to prevent transmission of HBV. More stringent precautions are necessary when treating persons likely to be infectious. Although the introduction of an immunization programme to protect dentists and clinical staff is imminent proper clinical hygiene will continue to be essential to safeguard both patients and clinicians.