Background Diesel exhaust emitted by internal combustion engines is a key source of urban air pollution. It is not just the traditionally-regulated total mass of particulate matter that is of public concern, but also ultrafine particles of pollution. These can readily penetrate deep into the lungs and pass through cell membranes into the bloodstream. Engine exhaust has adverse effect on many key bodily functions (respiratory, circulation and nervous system) and proximity to its source has been correlated with increased risk of tumours, asthma, various chronic respiratory ailments, heart attack, and other illnesses. Objectives The MEDETOX project’s main objective is to demonstrate innovative methods to assess the possible health risk connected with the exposure of the general public to diesel exhaust particles under real-life traffic conditions in the city of Prague. Diesel emissions from many thousands of trucks passing through large European cities represent serious health risks for the general public. In contrast to laboratory conditions, used in some previous and current studies, this project seeks to evaluate the toxicity of engine exhaust during operating conditions typical for core urban areas, where the engine emissions are of highest concern, as the aggregate dose is the highest. Specific objectives are: To identify the health risks related to emerging fuels and fuel additives and to demonstrate the use of standardised toxicity tests as an appropriate tool for regulatory decisions; and To build an effective interdisciplinary network targeted at the overall assessment of the health risk potential of engine exhaust during real-time operation of road vehicles and mobile machinery, and the monitoring of the effects of various policy decisions. This will be accomplished by a team of experts in the areas of engines and emissions (TUL), toxicity assessment (IEM) and public policy (ME).Expected results: The main result will be a set of standardised protocols for the sampling and toxicity testing of diesel emissions under various real-life traffic conditions. These will be used as tools for ‘hazard identification’ and ‘risk assessments’ based on the toxic effects of vehicle emissions. The protocols will include standard methodologies for: Sampling of engine emissions, particularly diesel exhaust under various traffic conditions; Testing cell toxicity of organic extracts from diesel exhaust (OEDE) particles in human lung cells (HEL); Testing genotoxic potential of OEDE in a cell-free model system; Testing genotoxicity of OEDE in human lung cells (HEL); Testing oxidative damage caused by OEDE in HEL cells; Cytogenetic analysis in HEL cells exposed to OEDE.The project will demonstrate the usefulness of these methodologies for environmental policy and governance in both the Czech Republic and in the EU. Substantial efforts will be made to disseminate the results of the project to national authorities (e.g. the Czech environment and health ministries, the National Institute of Health, and the Czech Inspection of Environment) and to the international authorities and other potential end-users such as the OECD, CONCAWE and the International Energy Agency (IEA).