The ELISPOT assay is particularly well suited to measure both clonal size and effector function of low-frequency antigen-specific T-cell populations directly ex vivo. Typically, an ELISPOT assay is performed with a freshly obtained sample (or cryopreserved sample) using less than 24h of culture. Additionally, this assay allows for the simultaneous analysis of hundreds of variables in parallel from a single tissue specimen. Because of these capabilities, this assay has found widespread use in the context of direct ex vivo immune diagnostic monitoring in humans. Herein we describe the rationale, methodology, and useful hints for performing T-cell epitope mapping using ELISPOT analysis, and review typical results of such an analysis.