From 1912 to 2003, 12,056 grey and red-legged partridges and pheasants found dead in the UK were examined. The trends in their infection rates with Heterakis species and histomonosis were strongly correlated among wild, pen-reared, young and adult partridges and young pen-reared pheasants but not adult pheasants. Except among the adult pheasants, the prevalence of Heterakis declined by 91 per cent to 100 per cent from 1952 to 1991. Heterakis isolonche was found predominantly in pheasants but only until the 1960s. Histomonosis declined relative to Heterakis species infections after the introduction of dimetridazole. There was a long-term change in the prevalence of Heterakis, with changes in domestic fowl husbandry being suggested as the cause.