This article reports a headspace gas chromatography (GC) method for the determination of the residual monomer in a methyl methacrylate polymer latex or emulsion. Because of the multiphase nature of a polymer latex, the level of the residual monomer cannot be quantified by headspace GC on the basis of its vapor-liquid equilibrium (VLE) without significant thermodynamic assumptions. With a significant dilution of a polymer latex sample followed by vapor-liquid equilibration at an elevated temperature, the monomer droplets are completely dissolved in the aqueous phase, and monomer absorption in the polymer particles can be minimized. Thus, VLE is established in the diluted latex, and a linear relationship between the monomer concentration in the vapor and aqueous phases can be obtained. This technique eliminates sample pretreatment procedures such as solvent extraction in the conventional GC method, and it avoids the risk of polymer deposition on the GC column caused by a direct injection of a monomer-containing solvent. It also eliminates the possibility of solvent interference in the conventional GC monomer analysis. This method is simple, accurate, and automated. (c) 2005 Wiley Periodicals, Inc.