Thirty-four nests of 11 species of birds containing eggs, and 38 nests of 12 species containing young of various ages, were used to determine the effect of applying DDT spray. Seventeen of the nests containing eggs and 19 of those containing young were left unsprayed as checks. The spray consisted of 1 pound of DDT to 2 pints of xylene diluted in fuel oil to make 1gallon, and was applied by a hand atomizer over an area of 1square foot surrounding and including each nest, at a dosage equivalent to 5 pounds of DDT per acre. This treatment evidently had no detrimental effect upon the hatching of eggs or development of young; it was not ohserved to cause abandonment of nests even when located in confined quarters.