Because this assay measures the final output of the upstream signaling pathway that controls the process, it has the ability to detect compounds that 1) inhibit TCR-proximal signals; 2) inhibit plasma membrane calcium channels; 3) inhibit plasma membrane potassium channels (which help maintain the driving force for calcium entry; 4) inhibit calmodulin; 5) inhibit calcineurin catalytic activity; 6) inhibit MAPKK; 7) inhibit ERK; or 8) inhibit PKC. In our previous work using TCRindependent chemical stimulation, we identified 160 compounds in the NIH's MLSMR that blocked lytic granule exocytosis. Among the 75 that were available for retesting, we found compounds that inhibited Ca 2+ influx, and thus could be Ca 2+ channel or K + channel blockers, compounds that inhibited MAPKK activity, and a compound that inhibited calcineurin activity and therefore could be either a calmodulin or calcineurin inhibitor. We were able to exclude the possibility that any compounds that we found that affected lytic granule exocytosis acted on PKC or on ERK catalytic activity. The assay also provides a rough measure of compound effects on cell viability by assessing changes in light scatter.