A direct intercomparison has been made between common tracer gases used to measure air infiltration rates in buildings. The results indicate that air exchange rates measured using sulfur hexaflouride, SF6, are slightly larger than those measured using methane, CH4, or nitrous oxide, N20. The ratio of air change rates measured using SF6 to air change rates measured concurrently using a lighter tracer gas was found to be 1.10 plus or minus 0.10.