Guaiazulene (7-isopropyl-1, 4-dimethylazulene) was heated at 350-600° for about 20 min in a quartz tube under nitrogen atmosphere. Above 450°, it was converted to 7-isopropyl-4, 5-dimethylazulene, 7-isopropyl-4, 8-dimethylazulene and unkown products. The yields of the former two products were the maxima at 550°.