This paper introduces the reports that follow it in a supplement dealing with the extended follow-up of mortality and cancer incidence among workers in the man-made mineral fiber (MMMF) production industry in Europe, the largest international study of its kind thus far initiated. In addition it reviews the prior epidemiologic evidence on this subject, both in terms of the earlier results of the same study and the results of other studies on the long-term effects of occupational exposure to MMMF. The conclusion drawn from this prior evidence was that the possibility that some excess of lung cancer may be causally related to exposure to MMMF could not be ruled out of the range of reasonable interpretations. When the findings of the extended follow-up, which this paper introduces, are added to the existing evidence, the overall results were considered to endorse the indication that no adverse long-term health effects have been detectable in terms of mortality throughout almost all segments of the MMMF production industry and to support the inference that MMMF--as present in the environmental conditions of early slag-wool/rock-wool production--may have played a role in the causation of lung cancer.