Wool was exposed to light of various wavelengths or was heated. The gases evolved were measured by mass spectrometry. At 254 m?, germicidal UV, the most complex variety-CO2, CO, H2S, and CS2, in descending amounts-was produced. At 365 m? “near” UV, a much simpler mixture of gases, CO2 and CO, resulted, At 436 m?, visible blue, only CO2 appeared. No gas was evolved at wavelengths longer than 436 m?. Heating in the dark at 160 degrees C produced H2O, CO2, CH4, CO, H2S, and COS. Thus, CO2 is the common gaseous product. Methane, produced only by heat, may account for the moderate flammability of wool.