Enzootic bovine leucosis is associated with infection by bovine leucosis virus. The incubation period is measured in years and a minority of infected animals develop clinical signs. The disease is widespread in Europe and elsewhere and can cause significant economic loss. The epidemiology is incompletely understood and findings from one cattle production system may not be directly applicable to another. Major control programmes exist in Denmark and West Germany and control schemes are being developed elsewhere. Eradication of enzootic bovine leucosis has been established as a goal in the EEC and research is revealing the ways in which this goal may be attained. To be effective, control and epidemiological monitoring must be interactive. Recently introduced serological tests, of improved sensitivity, provide a valuable tool.