Cytotoxic T-lymphocytes have received intensive scrutiny in the past decade, and have been implicated as important effector cells in diverse clinical settings. A variety of technological advances--the establishment of T cell clones, the production of MAb, the production of pure lymphokines through gene cloning, the modification of target cells by gene transfer and synthetic peptides--has led to tremendous strides in our understanding of CTL function and their role in the pathophysiology of a variety of disease states. It is likely that future efforts will generate important applications of such understanding, such as the pharmacologic modulation of CTL activity and proliferation, novel vaccines, and the introduction of adoptive transfer of cloned CTL as a clinically practical therapy.