This International Standard specifies a method for the determination, by gas chromatography, of the residual styrene monomer in reinforced plastics based on unsaturated polyester (UP) resins in the polymerized state. The residual styrene monomer content is an important criterion in evaluating the degree of cure of UP resins in the polymerized state. The method can also be used for the simultaneous determination of other volatile aromatic hydrocarbons in UP resins. The method is not applicable to UP resins of high chemical resistance.