Provides re-evaluations of the carcinogenic risks to humans posed by exposure to some 121 organic compounds, mostly industrial chemicals, selected from among the 834 agents evaluated in volumes 1-70 of the IARC Monographs series. Chemicals were selected for re-evaluation on the basis of considerable new evidence that might call for a change in the IARC classification of carcinogenic risk. The evaluations are presented in three parts. Part one provides full assessments of all relevant data on experimental carcinogenesis and cancer epidemiology for four chemicals: acrylonitrile 1 3-butadiene, chloroprene, and dichloromethane. Of these, 1 3-butadiene remained classified as probably carcinogenic to humans, and dichloromethane remained classified as possibly carcinogenic to humans. Acrylonitrile, previously classified as probably carcinogenic to humans, was reclassified as possibly carcinogenic. For chloroprene, previously judged not classifiable, new epidemiological evidence and new bioassays demonstrating carcinogenicity in rats and mice supported classification as possibly carcinogenic to humans. Part two re-evaluates 30 compounds for which new epidemiological or experimental carcinogenicity data were available and for which changes in classification were anticipated. Part three provides brief updates for 76 compounds and groups of compounds for which new evidence was restricted to experimental carcinogenicity data. As no new epidemiological evidence was available, and no reclassification was anticipated, these monographs reproduce the previous summary evaluations and update these with descriptions of new data.