Seventy fractions were obtained by vacuum distillation of a PCB mixture containing 42% of chlorine. Four of these fractions were chosen, the composition of which covered the whole of the observed region, and analysed by means of high-performance liquid chromatography (HPLC) on silica gel using n-pentane as the mobile phase and capillary gas-liquid chromatography (GLC) using OV-101 and Carbowax 20M as stationary phases at 200 degrees C. The chosen distillation fractions were further prepared by HPLC, each yielding 10-14 samples. Individual PCB standards and all samples were analysed by HPLC and capillary GLC. These procedures permitted the identification of those compounds which are eluted simultaneously under the conditions used in either HPLC or capillary GLC alone.