text: Fungal infections of the nasal cavity are a common cause of nasal disease in the dog and cat. Aspergillus fumigatus most commonly affects the dog; Cryptococcus neoformans is the most common fungus isolated from the cat. Rhinosporidium infection causes obstructive nasal polyps in the dog but has not been reported in the cat. Several other miscellaneous fungi, including Exophiala, Alternaria, Trichosporon, Blastomyces, and Histoplasma, and the alga Prototheca occasionally cause nasal disease in dogs and cats.