Common concern for the protection and improvement of the environment and the enhancement of human health and welfare underscore the purpose of this special report on the hazards of mercury directed to the Secretary's Pesticide Advisory Committee, Department of Health, Education, and Welfare. The report summarizes the findings of a ten-member study group and sets forth recommendations relating to major steps which should be taken in this country to define and correct the problem of mercury pollution. Currently, the problem is divided into two broad parts: one relates to the toxicity of unmodified mercury pesticiees and the other to accumulations in aquatic systems of alkylated mercury from a variety of sources, specifically methylmercury in fish and shellfish. Chapters deal with: medical implications of ingestion of mercury, microbial transformation of mercury, sources, distribution and control of mercury, ecological effects of methylmercury contamination, farming-food-forestry, airborne mercury, and analytical methods. Tables, figures, and references supplement the information. (BL)