Between 1848 and 1895 the melanic form E curbonaria of the peppered moth increased in Manchester from 0 to 98%. The reverse process is now occumng in one locality in Memyside where a year-to-year survey has shown that the pale form f. t@icu has increased from 6 to 30% between 1959 and 1984. Supporting information also comes from two studies in N Wales. The Clean Air Acts and the consequent decline in air pollution levels are probably responsible but there are many ill-understood problems, not the least being how, and the extent to which, non-visual selection operates.