The Eleventh Symposium on Advances in Tracer Method ology was held in Boston on October 13-14, 1966. The sym posium, which was sponsored by the New England Nuclear Corporation, commemorated the tenth anniversary of the Corporation. The Symposia on Advances in Tracer Methodology, which have been held regularly since 1957, bring together research workers in a variety of disciplines who share an interest in radioactive tracers. The four volumes, this one representing the record of the Eleventh Symposium, provide a compact and readily available source of information-much of which was usually scattered throughout the scientific literature-of inter est to biochemists, pharmacologists, endocrinologists, and analysts for whom tracers have become an indispensable tool. The editor is especially grateful to Dr. Konrad Bloch, Harvard University, and Dr. Waldo E. Cohn, Oak Ridge National Laboratory, for chairing the sessions at the Eleventh Sym posium. The cooperation of the speakers is deeply appreCiated. In addition, a special bouquet to my secretary, Mrs. Edith Thompson, for her generous assistance in arranging the various symposia and the publication of the papers. S. R.