Polystyrene sheets and foams and polycarbonate sheets were used. A known amount was placed in a combustion chamber of 12 liters in volume and combustion (candle type downward burning) was initiated by ignition with a Bunsen gas burner. The airflow through the combustion chamber was maintained at 17 liters/min and air was enriched with oxygen (30% O2) for the polycarbonate. The air exhausted from the combustion chamber was diluted and directed to a glass exposure chamber. (2.3 liters volume) to which was attached ifour tubes each containing one mouse with the head of the animal protruding in the exposure chamber. Characteristic decreases in respiratory rate were used as an index of sensory irritation of the upper respiratory tract and monitored during and following exposure to the combustion products. A dose-response relationship was obtained with all three materials and indicated that the combustion products of polystyrene films were the most irritating. When a known sensory irritant was incorporated into the polystyrene film prior to burning this addition was easily detected during exposure to the combustion products. It appears that the method used is sensitive enough to evaluate one of the possible effects of plastic decomposition products on the respiratory tract.