A series of 421 malignant pleural mesotheliomas, diagnosed in the Trieste-Monfalcone area, northeastern Italy, were reviewed. A large majority of the patients had been employed in "naval" work (shipbuilding, maritime trades, and dock work). Latency periods (time intervals between first exposure to asbestos and death), showed wide variations from one occupational category to another. Such variations were attributable, but only partly, to differences in the intensity of the exposure to asbestos. Various family cases were identified, including people with and without blood relationships. The data, obtained in the studies on Trieste-Monfalcone mesothelioma, suggest that interactions between asbestos and other factors play a considerable role in the pathogenesis of asbestos-related mesothelioma.