This International Standard specifies five methods for the measurement of the cloud Point of non-ionic surface-active agents. Methods A, B and C are applicable to non-ionic surface-active agents derived from ethylene Oxide by condensation with a lipophilic compound which has no oxypropylene groups. The selection of the method (A, B or C) depends on the temperature at which the aqueous solution of the product being tested becomes cloudy. Methods D and E are intended for use, after agreement between the Parties concerned, with products for which methods A, B and C prove unsatisfactory. Such products include mixed non-ionic surfaceactive agents such as those derived from ethylene oxide/propylene Oxide block copolymers. The selection of the method (0 or E) depends on the temperature at which the acid aqueous solution of the product being tested becomes cloudy. Method E is not applicable, however, to products derived from fatty acids or fatty-acid esters. NOTE 1 The cloud Point of products derived from fatty acids or fatty-acid esters tan only be determined if the repeatability of the determination is verified.