During the investigation of the foaming problem, the need for a rapid and sensitive method for detection of nonionic detergents was recognized. A number of methods are available for the determination of the ethylene oxide nonionic detergents in the higher concentration ranges. However, few methods are available for determination in quantities less than one ppm. Ammonium cobaltothiocyanate has been widely used to form a complex with polyethoxylated-type compounds since it was first described. The present method uses this reagent to give the typical blue color reaction on the thin layer. The sensitivity and selectivity of the method are comparable to that of Patterson et al. The method is applied to carbon adsorption samples representing 1,000 to 20,000 liters of water as well as 1 liter water grab samples. Whenever possible, as with most carbon adsorption samples, the analysis is confirmed by the PMA or the PTA method and infrared spectroscopy.