Over the past few years, research in the field of quantitative structure-activity relationships (QSAR) in chemistry, biology, pharmacology, toxicology, and environmental sciences has seen strong growth. New journals and books have appeared in each of these fields, however, the combination of QSAR and environmental sciences is still in its infancy. After the success of the Workshop on Quantitative Structure-Activity Relationships (QSAR) in Environmental Toxicology, held at McMaster University, Aug ust 16-18, 1983, with the proceedings publ ished in 1984 [QSA R in Environmental Toxicology, Kaiser, K. L. E. (Ed. ), D. Reidel Pub!. Co., Dordrecht, 406 p., ISBN 90-277 -1776-1], it was time to hold another workshop in 1986. Indeed, the response by the scientific community was excellent with over 50 participants from Canada, Germany, Great Britain, Hungary, India, Japan, The Netherlands, United States, and Yugoslavia. Moreover, both breadth and depth of papers given were significantly improved and the workshop discussions were intense and frank. Regrettably, the number of participants, number of papers given and submitted for these proceedings made it impossible to include the workshop discussions of these papers. However, several manuscripts were revised on the basis of these discussions and, therefore, do reflect this very interactive workshop. This volume presents the majority of papers given at the 2nd International Workshop on QSAR in Environmental Toxicology, held at McMaster University, June 9-13, 1986. Many of these papers contain primary, new scientific data, equations and results which will not appear elsewhere.