This supplement presents the papers submitted at the 27th meeting of the European Society of Toxicology, which was organised by the British Toxicology Society and held in Harrogate, England. As evident from the title of this book, the overall theme of the meeting was an exploration of some of the mechanisms of toxicity, as well as some models used in the investigation of toxic action. The topics dealt with can be grouped under four headings. The first of these, on the mechanisms involved in cell injury, was a joint symposium of the European Society of Toxicology and the Society of Toxicology of the United States of America. In the second group, mechanisms in carcinogen risk assessment were discussed. Mechanisms and models of teratogenesis was the subject of the third group of invited papers. Finally, a workshop on safety evaluation of biotechnological products dealt with present and future problems which this new area of technology poses for toxicologists. Short communications on recent studies and developments in toxicological techniques which were presented at the meeting are also included in this volume.