The gas phase pyrolysis of benzene was studied in a static system in the range 873–1036 K. The reaction is largely homogeneous, of order 1.5 and involves free radicals. The products are diphenyl and hydrogen. The Arrhenius plot curves slightly at lower temperatures, but at higher temperatures the rate may be represented by d[h2]/dt=k[c6H6]. where k= 109.83 exp (–225 kJ mol–1/RT) dm mol–½ s–1. The results are interpreted in terms of a simple chain reaction and compared with the results and mechanisms of other workers. The simple mechanism represented the results as well, if not better, than the more complicated mechanisms which have been proposed. Above 1036 K, ring opening occurs and acetylene, ethylene, methane and carbon are formed. A range of polyphenyls and polynuclear aromatic hydrocarbons were detected on the carbon and may be intermediates in soot formation.