It has been suggested that asbestos might have an important role in the development of p53 mutations in mesotheliomas. The objective of this study was to examine asbestos-associated mesotheliomas and non-asbestos-associated mesotheliomas to establish whether the frequency of p53 immunostaining and, by implication, p53 gene mutation is related to asbestos exposure. Immunopositivity for p53 was found in seven (44%) of the 16 mesotheliomas examined. The frequency was approximately the same in both the asbestos-associated mesotheliomas and the non-asbestos-associated mesotheliomas. It is concluded that the frequency of p53 immunostaining in mesotheliomas and, by implication, the frequency of p53 gene mutation is probably not related to asbestos exposure.