The results of an ultraviolet photoelectron spectroscopic study of the thermolysis of 5,5-dimethyl-1-phenyl-Δ3-1,3,4-triazoline-2-thione (1) are presented. That CS2 is one of the major products establishes that carbon monosulfide (CS) is formed as a reaction intermediate in the thermolysis. Other products of thermolysis of 1 are molecular nitrogen and isopropylidenephenylamine (2). The photoelectron spectrum of the latter is also reported. Thermolysis of 1 in solution also leads to CS, which polymerizes extensively in the absence of trapping agents but is partly converted to CS2 in the presence of S8 and to COS in the presence of cyclohexanone.