Three cases of malignant pericardial mesotheliomas are presented with evidence of occupational asbestos exposure. Examination results are compared with findings from experimental and epidemiological research on biological effects of asbestos dust. There are sufficient indications that time-limited effects of asbestos dust established either by measurements or assessment of the amount of concentration after a latency of more than 20 years are apt to result in the development of mesotheliomas of the pleura and peritoneum and, moreover, the pericardium. It is suggested that malignant pericardial mesothelioma also be recognized as another form of occupational disease caused by asbestos dust.