This is not, nor is it intended to be, either a textbook or complete reference book of medical parasitology. Rather it is made up of fourteen more or less independent summaries of recent experimental work in fourteen more or less related aspects of medical parasitology which were originally presented as a symposium of the New York Academy of Medicine on March 15 and 16, 1949. The fourteen different authors were selected because each had had particular experience in the aspect of the subject which he presented. Each author, thus, should be able to write with the weight of authority on the subject covered. For the most part, this is true not only with reference to his own work but in the review of the literature as well. Even a review such as this, however, may be outdated by the time it appears.