Abstract Increases of leukaemia in young people that cannot be explained in terms of radiation have been recorded near both of Britain's nuclear reprocessing plants at Dounreay and Sellafield. These were built in unusually isolated places where herd immunity to a postulated widespread virus infection (to which leukaemia is a rare response) would tend to be lower than average. The large influxes of people in the 1950s to those areas might have been conducive to epidemics. The hypothesis has been tested in Scotland in an area identified at the outset as the only other rural area that received a large influx at the same time, when it was much more cut off from the nearest conurbation than at present—the New Town of Glenrothes. A significant increase of leukaemia below age 25 was found (10 observed, expected 3·6), with a greater excess below age 5 (7 observed, expected 1·5).