Follicular helper T (Tfh) cells are the helper T-cell subset that localizes in germinal centers within secondary lymphoid organs. They support B cells to produce high-affinity antibodies and generate B-cell memory. By contrast, follicular regulatory T (Tfr) cells localize in germinal centers to suppress B-cell responses. Coordinately regulating antibody responses, Tfh and Tfr cells play a critical role for vaccination, infectious disease control, and the development of autoimmune diseases. Although bona fide Tfh and Tfr cells are hardly detected in human blood, circulating Tfh and Tfr memory cells in blood can be used to investigate their functions in health and disease. We have developed a comprehensive flow cytometric analysis to define different circulating Tfh and Tfr populations within CXCR5⁺ CD4⁺ T-cell population in human blood, based on numerous cell surface markers including CD25, CD127, CCR7, PD-1, CXCR3, and CCR6.