Measurement of ''immunity'' has often focused on measurement of humoral immunity to determine the presence of protective antibodies. Cellular immune function is fundamentally more complex and difficult to measure. Chapter 9 emphasizes the importance of the rationale for undertaking immune assessment to selecting the appropriate assessment method. It also provides a brief description of a variety of in vivo, and in vitro assessment methodologies. The use of whole-blood cultures for evaluation of functional activity of lymphoid cells in vitro is explored in Chapter 10 with an emphasis on the feasibility of their use for field studies.