The constant concentration tracer gas (CCTG) technique is typically used to measure air infiltration rates in mulitzone buildings. The measurements are performed by injecting metered amounts of a tracer gas into each zone so as to keep all the zones at a target concentration. One drawback to this method is that no information is gained about the level of interzone flow rates in the building. Modified constant concentration techiques are described which allow selected infiltration and interzone air flow rates to be estimated. These techniques differ from the typical operation in that there are certain zones where no tracer gas is injected. One approach, described as discontinued injection, is useful for measuring interzone flow rates between two sections of a building when the air flow rates are relatively constant. The tracer gas injection in one of the sections is stopped at a certain point in time, but the concentration measurements are continued. The increase of tracer gas injection in the other section and the drop in concentration in the "starved' section are used to estimate the air flow rates between the sections. Field measurements using the modified CCTG methods are presented for experiments in single family and multifamily buildings. The results are compared to those obtained by passive, multiple tracer gas tests.