The Bureau of Entomology and Plant Quarantine, United States Department of Agriculture and the Wyoming Department of Agriculture carried out a grasshopper control program on approximately 300,000 acres of Wyoming range land during the summer of 1951. Aldrin (Compound 118) was used as the toxicant. Two ounces of Aldrin per gallon of kerosene were sprayed from aircraft at the rate of one gallon of insecticide to the acre. The use of Toxaphene and Chlordane on bran for grasshopper control had previously been found to cause an increased mortality on game bird populations (Post, 1951 a). The Wyoming Game and Fish Commission was interested in knowing the possible deleterious effects of Aldrin spray on game birds. Prior to the actual spraying operations, a series of pheasants were given oral doses of known amounts of Aldrin. The