Total and asbestos lung fibre burdens were identified and quantified in a case-control study of 100 patients who included 20 subjects with pleural mesothelioma, matched for age and sex with four other pathological series of 20 patients each. These series respectively had squamous cell carcinoma, lung adenocarcinoma, lung metastasis and cardiovascular diseases. The study was conducted with no prior knowledge of past exposure. The highest concentrations of asbestos bodies were found in the mesothelioma series, and in 70% of these cases exceeded 1000 asbestos bodies per gram of dry lung tissue. Eighteen species of natural and synthetic uncoated fibres were found. Except in the mesothelioma cases, the numbers of non asbestos fibres and asbestos fibres were similar. The concentrations of chrysotile fibres were identical in all five pathological series. Amphibole fibre retention was higher in the mesothelioma cases versus the controls, both for amosite and crocidolite. The predominant retention of amphibole fibres in tissue is discussed.