A case of mesothelioma, apparently arising in the pericardium, is reported in a patient who, 15 years previously, had been treated for angina pectoris by dusting of the pericardial cavity with a mixture of fibrous dusts. At autopsy, transparent fibers and ferruginous bodies were present within the pericardium. Electron diffraction and microprobe analysis indicated that approximately two thirds of the fibers were tremolite and anthophyllite asbestos, and the remainder, fiber glass. Development of mesothelioma in laboratory animals has been reported after intrapleural deposition of asbestos and other fibers, but in humans, the link between exposure to asbestos and mesothelioma has always been based on epidemiologic data and the retrospective finding of asbestos in tissues. To our knowledge, this is the first example of a malignant mesothelioma in a human associated with direct mesothelial contact with fibrous dusts.