The current English literature through 1984 on the products of pyrolysis and combustion from polystyrenes and the toxicity of thoseproducts is reviewed. Among 57 compounds detected by chemical analyses of the thermal decomposition products produced under various atmospheric conditions (vacuum, inert and oxidative), the main volatile component is the styrene monomer. Evidence is provided that the mass fraction of styrene increases with furnace temperatures at least through 500ºC. At 800°C and above, the concentration of styrene decreases. In oxidative atmospheres, carbon monoxide (CO),carbon dioxide (CO2) and oxidative hydrocarbons are formed. The concentrations of CO and CO2 are in function of temperature and combustion conditions, i. e. greater amounts are produced in theflaming than in the non-flaming mode. Eleven different test procedures were used to evaluate the toxicity of the pyrolysis and combustion atmospheres of polystyrenes. The more toxic environments produced under flaming conditions appear to be mainly attributed to CO and CO2 but rather to some other toxicant, probably the styrene monomer. When compared with other common materials used inbuildings and residences, polystyrenes, in general, are among the least toxic.