This volume represents a collection of pioneering papers introducing immunochemical techniques to the aquatic sciences. It is the product of a workshop entitled "Immunochemical Approaches to Coastal, Estuarine and Oceanographic Questions" held at the University of Southern Maine, Portland, Oct. 5-7, 1986. Funding from many sources made this workshop possible, and is gratefully acknowledged. The reader will note great variability in both the quality and scope of the papers which we have divided 'into four sections: I. Background material on the immune system (borrowed from a recent NIH publication) II. Background material related to aquatic sciences III. Techniques IV. Applications Readers familiar with terminology are directed to start with the original contributions related to aquatic sciences, page 21. Some of the contributions are abstracts only. Others are preliminary, for which we are grateful to the authors for their willingness to share recent sometimes tentative findings with a broader community. Some offer novel and tempting insights, but as they exist, lack adequate standards and controls. Others are thorough and represent major scientific contributions. The promise rests in generating and working with reagents of great specificity enabling orders of magnitude improvements in the sensitivity of our measurements. Authors also address the problems and limitations. We thank the numerous authors and reviewers. In support of every successful endeavor is someone of unusual savvy. For us, this has been David A. Phinney. His leadership, wisdom and wit have been important to the introduction of flow cytometry/sorting and immunochemistry into aquatic research.