Fingerling channel catfish (Ictalurus punctatus) offered diets containing 0.04–4.0 μg endrin/g food (dry weight) rapidly accumulated the pesticide. Amounts in the tissues were directly proportional to amounts in the food. Dietary endrin had no measurable effect on growth or mortality. After endrin was withdrawn from the diet, it rapidly disappeared and could not be detected after 41 days. In fish exposed to 0.5 μg endrin/liter of water, mortalities began at tissue levels of 0.7 μg endrin/g of wet whole fish and total mortality occurred at levels near 1.0 μg/g.