The use of pyrethrins, allethrin, and possibly furethrin as a coating on paper and cloth bags for the protection of stored for products against insects has created a need for a sensitive, accurate, and rapid method of detection and determination of these materials. Such a method might also find use in the determination of residues on food products and in the analysis of concentrates and various formulations. A colorimetric method developed for the estimation of small amounts of pyrethrins, allethrin, and furethrin is sensitive to about 200gamma and has an average experimental error of about 4per thousand. The color reaction on which the method is based can also be used as a color test and can possibly be developed into a colorimetric determination of other cyclic alpha,beta-unsaturated ketones. The method outlined can be used only if it is known which insecticide (pyrethrins, allethrin, or furethrin) is present. Further, if more than one of these insecticides is present it is impossible by this method or any other method published up to the present time to determine the concentration of each insecticide specifically.