Samples of moths have been taken in the Manchester area at sites in localities with moderate to extreme atmospheric pollution. The majority of species collected are dark in color, many typically pale species being represented by dark variants. Four species polymorphic for melanic and non-melanic morphs have been examined in more detail. In Biston betularia the melanic frequency is over 93% at all stations, but the frequency of typicals appears to have increased over the past 15 years. This coincides with a period of extensive smoke control zonation. Gondontis bidentata has a higher frequency of melanics than has been recorded elsewhere in the country. There is significant variation between sites, the higher frequencies occurring in the more polluted localities. Non-melanics segregate into a pale and a dark category. In reared samples males exhibit a greater frequency of melanics than females.