Vaccination of health care workers is highly effective in preventing occupationally acquired hepatitis B virus (HBV) infection, but cost is a major factor impeding routine immunisation programmes. Pre-vaccination serological screening may be cost-beneficial if the prevalence of immunity is sufficiently high to offset its cost against the consequent reduction in vaccination needs. This critical population prevalence can be calculated given the cost of vaccination and testing. Samples of health care worker populations were examined for immunity and, using local present-day costs, it was calculated that pre-vaccination screening would be cost-beneficial in black nursing and laboratory personnel, but not their white counterparts or any student health care workers.