An attempt has been made to establish the testing of household insecticides on a sound and comparable basis. The necessity for the reduction of variables to a minimum is pointed out and it is suggested that a definite standard be adopted for time, temperature, humidity, insecticide concentration, spray concentration, pressure in sprayer, air condition, angle of spray, kind of insect, and condition of insect. Emphasis is placed upon the fact that many tests and extended observations are necessary and explicit directions for conducting tests upon flies are given.