(14)C-dioxin tracers were used to evaluate whole MM5 sampling train recoveries of dioxin and to determine the distribution of dioxins spiked into a sampling train that was concurrently sampling emissions from a burn of either natural gas ('clean' burn) or kerosene ('dirty' burn). The spike tests were made with a pilot-scale furnace constructed and operated in the laboratory. Recovery of (14)C-dioxin from the MM5 sampling train was determined by scintillation spectrometry. The experimental results indicate that the amount of spiked TCDD-(14)C recovered was approximately 85% during a natural gas test and 83% during a kerosene test. The amount of spiked OCDD-(14)C recovered was approximately 88% during a kerosene test. Also, the data indicate that during the kerosene tests OCDD-(14)C is collected primarily in the front half of the sampling train but TCDD-(14)C is often found in the XAD and the rear filter bell, riser and condenser of the sampling train. During the natural gas tests, TCDD-(14)C was primarily in the XAD. The distribution of the TCDD-(14)C in the kerosene tests was dependent on the rigid operation of the sampling train. The information from the study will be used to determine procedural areas that need improvements or modifications to allow the efficient collection and accurate determination of trace levels of dioxins and furans using the MM5 Method.