Abstract Between September 1982 and January 1983 lung, heart and liver samples for histological examination were obtained from 170 free-living stags and hinds and from 78 farmed stags. A further eight liver and four lung samples were collected from additional wild stags. Protostrongylid eggs and larvae were present in 76% of the wild deer lungs but in only 4% of the farmed deer. Fourteen per cent of the wild deer showed an interstitial pneumonia associated with the protostrongylid infection. Conversely, pulmonary lesions of the type associated with Dictyocaulus spp. were extremely common in the farmed deer but only 12 free-living animals had dictyocaulus-type lesions. Sarcocysts in the myocardium, with or without accompanying interstitial cellularity, affected 42% of the wild deer and 4% of farmed deer. Parasitic lesions in the liver were found in 3% of wild deer and 21% of farmed deer.