Because of the political, social and environmental problems associated with dependency on fossil fuels, there is considerable interest in alternative energy sources. Hydrogen is regarded as a promising option, particularly as a fuel for road vehicles. The Dutch Energy Research Centre (ECN) recently published a vision of the future, in which it suggested that by 2050 more than half of all cars in the Netherlands could be running on hydrogen. A switch to using hydrogen as the primary energy source for road vehicles would have far-reaching social consequences. As with all technological developments, opportunities would be created, but drawbacks would inevitably be encountered as well. Some of the disadvantages associated with hydrogen are already known, and are to some degree manageable. It is likely, however, that other drawbacks would come to light only once hydrogen-powered cars were actually in use. With that thought in mind, and in view of the social significance of a possible transition to hydrogen, it was decided that the Health Council should assess the positive and negative effects that hydrogen use could have on public health. It is particularly important to make such an assessment at the present early stage in the development of hydrogen technologies, so that gaps in existing scientific knowledge may be identified and appropriate strategies may be developed for addressing such gaps. This report has been produced by the Health and Environment Surveillance Committee, which has special responsibility for the identification of important correlations between environmental factors and public health.