FOLLOWING the basic work of several investigators in establishing the relationship between the anterior pituitary and the thyroid, experimental hyperthyroidism was produced in many animals by implants, or by injections of suspensions and extracts of the hypophysis. Hyperthyroidism and concurrent exophthalmos, a situation resembling Graves’ disease, was produced experimentally by injecting pituitary emulsions in ducks (Schockaert, 1931). Later, similar results were obtained in guinea pigs by Loeb and Freedman (1932), and Friedgood (1934). The purpose of this paper is to report in detail a series of experiments wherein a remarkably rapid exophthalmos can be produced in Fundulus, the common Atlantic “minnow.” Some of these experiments were done several years ago, and reported in abstract form (Abramowitz and Fevold, 1937; Abramowitz, 1940). In addition to these earlier experiments, recent observations3 are also included.