One of the problems that plagues a building energy audit is getting an adequate estimate for one key element--air infiltration. Often this energy loss is attributed to any discrepancy between calculated and actual measured energy use. The question of how simple air infiltration measurement techniques could assist the auditor brought about the development reported here. Container samples, in this case plastic bottles, are used to evaluate air exchange rates in a variety of buildings, making use of the tracer-gas technique. The method is simple enough that it is possible to mail the sample bottles to the occupants and to the laboratory.