Two genera of lung nematodes were found in a sample of 382 wild ringed seals (Phoca hispida). Otostrongylus circumlitus were found mainly in young of the year where they occupied the main stem bronchi causing extensive mucus production, mucosal hyperplasia and peribronchitis. Immature stages of the nematode were found in pulmonary vessels causing endarteritis. There was only a slight reduction in respiratory parenchyma in infected seals and no correlation between infection and size or body condition. However, the sharp decline of O. circumlitus infection from 32% in young of the year to 0.5% after the first winter suggests that this parasite may play a role in the population dynamics of ringed seals. Filaroides (Parafilaraides) hispidus was found in alveoli of seals throughout all age classes causing no significant lesions. The infection rate increased from 44 to 71% in the 7 to 13-yr-old animals and declined to 38% in older seals. Concurrent infections occurred in 28% of young of the year seals.