In a mesothelioma case-control study, asbestos and other mineral fibers from lung burden were examined as causal factors. Diagnosis was confirmed by a panel of pathologists. For 66 cases and 66 controls from hospitals in five German towns, lung tissue fiber analysis by transmission electron microscopy was available. Control patients were treated by a surgical lung resection mostly because of lung cancer. For chrysotile and other mineral fibers a significantly increased odds ratio (OR) was not observed. A clear dose-response relationship was demonstrated for the concentration CA of amphibole fibers longer than 5 microm. Between 0.025 and 2.5 fibers/microg dry weight (f/microg) the relationship can be approximated as OR = CA/(0. 025 f/microg). Similar but less distinct dose-response relationships were found in a Canadian and an Australian study. It is concluded that among German mesothelioma patients factors not associated with amphibole fiber concentration are not predominating.