Good resolution of mixtures of mono-and di-carboxylic free fatty acids can be obtained using Carbowax 15–20,000-isophthalic acid on a support modified with hexamethyldisilazane. Previously numerous stationary phases have been used to chromatograph free fatty acids. We now have tried to consider all operating parameters to minimise the tailing of peaks and have devised a method suitable for the analysis of mono- and di-carboxylic acids.