The present compendium of data profiles for chemicals for the evaluation of their hazards to the environment of the Mediterranean Sea is a first attempt by the International Register of Potentially Toxic Chemicals (IRPTC) to address this very difficult problem of presenting the necessary data for environmental hazard evaluation of chemicals to experts in the several disciplines of science concerned with environmental hygiene. While this document is addressed to the Mediterranean Action Plan for further development of its Draft Protocol for the Protection of the Mediterranean Sea Against Pollution from Land-Based Sources, it could be addressed equally well to any of the other international conventions which deal with the prevention of chemical pollution of the seas.