Pentachlorophenol and its salts are used as biocides. Although they are used mainly for preservation and treatment of wood, their antimicrobial, antifungal, herbicidal, insecticidal and molluscicidal properties led to a widespread application of PCP formulations. Bevenue and Beckman reviewed the literature up to 1967 on the chemistry, toxicology and environmental residues of PCP (Residue Rev. , 19: 83- 134, 1967). Significant advances in analytical methodology, recurrent incidents of mortalities of non-target organisms exposed to PCP, regulatory actions pertaining to PCP usage in countries such as Japan and Sweden, and detection of the ubiquitous distribution of PCP in the environment, added to the wealth of recent literature on pentachlorophenol. In spite of the usage of PCP as an antimicrobial agent in drilling and packer fluids during oil-drilling operations in the marine environment, little is known of the toxicity of PCP to marine and estuarine organisms. The purpose of this volume is to present up-to-date information (including a number of new studies on marine and estuarine organisms) on the chemistry, pharmacology and environmental toxicology of pentachlorophenol. This volume is a collection of papers presented at an international symposium sponsored by the U. S. Environmental Protection Agency and The University of West Florida, held at Pensacola Beach, Florida, June 27-29,1977. I am grateful to Norman L.