Ethoxylated nonylphenol (Rokaphenol NX-8) with a mean content of 9 oxyethylene groups was subjected to fractionation by adsorption column chromatography. The fractions obtained with a different mean polyether chain length as well as nonseparated Rokaphenol were removed from their aqueous solutions of various concentrations in a foaming column. A correlation was found between the effect of foaming and the oxyethylation degree; namely, the lower the content of oxyethylene groups in the compounds, the better the result of foaming. This is true, however, merely in the case of compounds which dissolve well in water. If the content of oxyethylene groups is so low that it diminishes the solubility of the detergent in water, foaming proceeds much more poorly.