IT is well known that myxomatosis has caused a high mortality among wild rabbit populations in most parts of England and Wales, and in those parts of Scotland and Ireland to which the disease has spread. Where it has been possible to make accurate observations, a mortality-rate of about 99 per cent was found. A similar death-rate was usual in Australia during the first year (1950–51) of their epizootic, but attenuated strains were found from 1953 onwards1.