Abstract: Disclosed is a process and test kit for determining the reliability of a barrier to microorganism passage. In accordance with the process, a multiplicity of non-self replicating particles is introduced into a first gas volume, disposed on one side of a barrier to particle movement, and particle traps are placed in a second gas volume on the other side of the barrier. The particles carry a marker substance such as a toxin for a selected microorganism or a component needed for growth of a selected microorganism. The barrier is operated and the contents of the trap are assayed for the amount of the marker substance present in association with particles which crossed the barrier by adding the marker substance in the trap to a culture of the selected microorganism and detecting the effect of the marker substance on the culture. Finally, the results of the assay are compared to a standard to determine the number of trapped particles which crossed the barrier.