A number of cats in an experimental colony showed signs of respiratory disease. One 4-month-old animal died after showing dyspnoea and was necropsied approximately 12 hours after death. Pale grey consolidation of the ventral two-thirds of both lungs was observed. Within the consolidated areas there were grey foci ranging from 1 mm to 2 cm in diameter. There was a purulent exudate in the trachea and primary bronchi, and the bronchial lymph nodes were enlarged. Microbiological findings are discussed.