From 1979 to 1985, protostrongylid infections (small lungworms) of chamois were studied at the Bauges hunting reserve, in the western Alps. Fifty-two chamois were necropsied on 24 sites and lung nematodes identified to species. From June to November 1985, a more detailed study was undertaken on four sites where chamois were the only ruminants. First-stage larvae excreted in feces and infection of snails intermediate hosts were monitored. The protostrongylid species were, arranged in decreasing order of prevalence, Neostrongylus linearis, Protostrongylus rupicaprae, Muellerius capillaris, and Muellerius tenuispiculatus. Intensity was higher in females than in males (in chamois aged 4 to 11 months compared with younger or older ones) in winter than in the other seasons. Intensity of infection increased as chamois were located at lower altitudes. The snail intermediate hosts were, in decreasing order of importance, Helix pomatia, Cepaea sylvatica and Arianta arbustorum.