Since 1996, three primates newly arrived at London Zoo have been found to be infected with hepatitis B virus. The species involved were white-cheeked gibbons (Hylobates leucogenys leucogenys and Hylobates leucogenys siki) and a western lowland gorilla (Gorilla gorilla gorilla). The protocols for the practical management of these cases, including the immunisation of susceptible non-human primates and the staff with recombinant hepatitis B vaccine are described, and the origin and evolution of hepatitis B infection in primates are discussed.