Our ability to analyze T-cell function in vitro has progressed in recent years to include analysis of early signaling events, such as specific protein phosphorylation, intermediate functions, such as degranulation and cytokine production, and later functions, such as proliferation. Many assays are now available to monitor these events, and comparative studies of some of these assays have been published. Major recent developments in this area include the ability to measure T-cell degranulation via cell surface exposure of CD107 and the use of polychromatic flow cytometry to examine multiple phenotypes and functions of responding T cells.