Chemical pesticides continue as a point of major controversy in our society. Increasingly stringent regulatory actions on the part of state and federal agencies, exemplified by the RPAR (Rebuttable Presump tion Against Registration) program of the Environmental Protection Agency, are supported by environmental groups and are generally op posed or viewed with skepticism by agriculturalists. The energy crisis invokes other questions on benefits of pesticides versus nonchemical controls and effects on labor utilization. As DDT and other persistent pesticides have been phased out, the more labile, short-lived chemicals have filled the voids in pest management systems; and effects on nontarget species appear to have declined in recent years as the shift occurred. However, nagging ques tions of the hazard to man and other nontarget species from long-term, low-level exposure to pesticides are frequently raised; and recent suggestions that certain well-known and long-used chemicals cause cancer, increase sterility, and initiate or augment other deleterious effects in test animals have instilled a sense of caution and raised con cern about the continued availability of some pesticides previously considered safe. So the facade of concern and confusion continues. This book is an outgrowth of a symposium at the meeting of the American Association for the Advancement of Science in February, 1978. An introduction has been added, and some of the papers have been modified since presentation.