Book excerpt: This volume of the IARC Monographs provides evaluations of the carcinogenicity of bitumens and their emissions, the N-heterocyclic polycyclic aromatic hydrocarbons benz[a]acridine, benz[c]acridine, dibenz[a,h]acridine, dibenz[a,j]acridine, dibenz[c,h]acridine, carbazole and 7H-dibenzo[c,g]carbazole, as well as the S-hetrocyclic polycyclic aromatic hydrocarbons benzo[b]naphtho[2,1-d]thiophene and dibenzothiophene. Bitumens are produced by distillation of crude oil during petroleum refining, and also occur naturally. Bitumens can be divided into six broad classes, according to their physical properties and specifications required for different applications. The major use (about 80%) of bitumens is for road paving; other uses include roofing, waterproofing, sealing and painting. The term "bitumen" should not be confused with "asphalt", which refers to the mixture of bitumen (4-10% by weight), small stones, sand and filler used for road paving. Bitumens are complex mixtures that contain a large number of organic chemical compounds. Application of bitumens may generate emissions (fumes and vapours) that may contain, among volatile and non-volatile compounds, a number of known or probable carcinogens. An IARC Monographs Working Group reviewed epidemiological evidence, animal bioassays, and mechanistic and other relevant data to reach conclusions as to the carcinogenic hazard to humans of various occupations that entail exposure to bitumens and bitumen emissions, including road paving, roofing, and application of mastic asphalt, and to various heterocyclic polycyclic aromatic compounds.