Malignant mesothelioma is an uncommon, but increasingly important, neoplasm. The existing English-language medical literature concerning non-asbestos-related malignant mesotheliomas was reviewed for evidence of other agents associated with the induction of malignant mesothelioma. Both animal and human data were reviewed. In most reviews of malignant mesothelioma, there are a significant proportion of cases without documented asbestos exposure (range, 0% to 87%). Furthermore, there are several fairly well-documented agents other than asbestos that induce malignant mesothelioma in animals, and strong evidence exists that such is the case in man. In reviews of malignant mesothelioma, the percentage of cases with asbestos exposure varies, but a significant number are apparently not asbestos related. It is believed that sufficient evidence exists to suggest that non-asbestos agents can induce malignant mesotheliomas in man, and additional epidemiologic studies in this area are needed.