Pleural mesothelioma has been diagnosed in 52 patients in three hospitals on Merseyside between 1955 and 1970, 60% being diagnosed from operation specimens and the rest from postmortem tissues. Necropsies eventually held on nearly half the operation cases confirmed the diagnosis, giving a necropsy rate of 70% for the series. The morbid anatomy conformed to earlier descriptions except that widespread metastases were much commoner than has usually been described. Histological findings agreed with previous accounts of the tumour, except that, in our hands, special acid mucopolysaccharide staining was less reliable than Southgate's mucicarmine, which was of value in differential diagnosis. Association with asbestos was confirmed from industrial histories in 80% of cases, the commonest industries involved being shipbuilding and repairing in men and sackware repairing in women. Lungs of industrial mesothelioma cases showed basal asbestosis in 17% and excessive asbestos bodies in almost all the rest. Quantitative comparison of asbestos bodies in lung smears from mesothelioma cases compared with lung smears from other Merseyside adults showed much higher counts in the mesothelioma cases. The interval from first exposure to asbestos until appearance of mesothelioma ranged between 13 and 63 years, with a mean of 42 years. We think the incidence of mesothelioma will continue to rise with the increased use of asbestos until about 40 years after adequate protective measures have been taken.