Benzene. The evidence for carcinogenicity of benzene in humans was evaluated by the IARC in 1982 as follows: "It is established that human exposure to commercial benzene or benzene-containing mixtures can cause damage to the haematopoietic system, including pancytopenia. The relationship between benzene exposure and the development of acute myelogenous leukaemia has been established in epidemiological studies. "Reports linking exposure to benzene with other malignancies were considered to be inadequate for evaluation. "There is sufficient evidence that benzene is carcinogenic to man." This evaluation now warrants some elaboration and updating. While the epidemiological evidence concerning benzene carcinogenicity is strongest for acute myelocytic leukaemia, there is some limited evidence of increased risks of chronic myeloid and chronic lymphocytic leukaemia. In addition, recent studies have suggested an increased risk of multiple myeloma, while others indicate a dose-related increase for total lymphatic and haematopoietic neoplasms. Corroborative evidence for such a generalized effect comes from experimental studies showing that exposure to benzene depresses all lympho-haematopoietic cell lines. While only limited evidence of benzene carcinogenicity in experimental animals exists, the recent findings of the National Toxicology Program (NTP, 1984) in the U.S.A. and Maltoni et al. (1985) strongly indicate that benzene is an experimental carcinogen. Toluene and xylene. While no direct human evidence is available, there is recent evidence of carcinogenicity of toluene and xylene at high concentrations in experimental animals. It should also be noted that any future epidemiological observations of cancer risks associated with toluene or xylene would have to take account of the suspected effects of benzene impurities.