The prevalence of antibodies to hepatitis B virus (anti HBs or anti HBc) was 16.9 per cent in a group of anaesthetists, compared to 3.7 per cent in volunteer blood donors and 5.6 per cent of patients without hepatic infections. Professional risk factors such as treating a hepatitis B patient or working in a hospital laboratory, haemodialysis, an intensive care unit, or in oncology, did not correlate with antibody prevalence. Personal risk factors such as a history of a family member with hepatitis, or of receiving blood transfusion in the past were also not associated. A greater number of anaesthetists with a history of hepatitis in the past had antibodies, than those with no history (p less than 0.05). The country of origin may have been a contributing factor to antibody prevalence as highest positivity rates were found in subjects from Asia, Africa and Eastern Europe. One of 31 (3.2 per cent) seronegative subjects seroconverted over a four-year period. Results of testing in 1978 and 1982 revealed that 37 per cent of immune subjects possessed only anti HBc and at least one person positive for both markers on the first occasion was only anti HBc positive later. Laboratory testing, risk factors, and immunization for HBV should be examined in greater detail in larger populations of health care workers.