It is thought that the extremely high occurrence of malignant pleural mesothelioma in the two Turkish villages of Karain and Tusköy could be related to environmental zeolite fibers. Mineral fibers were assessed in lung samples from two cases of malignant pleural mesothelioma in Tusköy, using the light microscope and the analytical transmission electron microscope. Zeolite (erionite) fibers and ferruginous bodies, formed around zeolite fibers (zeolite bodies), were frequently encountered in these samples. Under the light microscope, zeolite bodies were morphologically identical to typical asbestos bodies. To document the zeolite exposure in this area of Turkey, it is suggested that a biologic monitoring study be performed in villages in which mesotheliomas occur and in control villages, by testing for the presence of zeolite bodies in sputum.