Orally administered Linguatula serrata nymphs attached themselves to the pharynx, larynx, trachea and bronchi of various animals, and the symptoms evoked were similar to those of halzoun and the marrara syndrome. Nymphs persisted for the longest period in rabbits, in which some growth occurred. In previously egg-infected animals the reaction to introduced nymphs was more marked than it was in normal animals. Nymphs migrated to the pharynx of rabbits and dogs when deposited in the stomach. Examination of the liver and lymph nodes of goats and sheep showed the goat to be the more commonly and heavily infected. In Lebanon the mesenteric lymph nodes probably provide a major source of infection in man. The rate of adult L. serrata infection in 30 stray Beirut dogs was 43.3%. Local anesthetic and antihistaminic drugs are suggested for treatment of halzoun.