Epidemiology has greatly contributed in the past to the recognition of work-related ill health. Working life, work organisation and labour markets are now rapidly changing. Does epidemiology still have a relevant role in this evolving context? New exposures at the workplace and related health and behavioural changes currently prevailing in industrialized countries are reviewed. It appears that epidemiology might in the future play an even greater role than in the past, when the mere observation of a few subjects could sometimes lead to the identification of occupation-related risks. In order to examine the relations between complex and low-level exposures and subtle and long-term risks in working populations, epidemiology appears essential. Controlled, longitudinal population studies are especially needed to clarify, for prevention purposes, the meaning and the predictive role of the increasing number of markers of exposure, of effect and of individual susceptibility; to describe and model in quantitative terms exposure-response relations; to assist with risk assessment and evaluation. Although occupational health research has a long tradition of inter-disciplinary co-operation, this remains a major challenge for the future.