In recent years there has been a tremendous expansion in our understanding about CD8⁺ T cells. We now know that, as for CD4⁺ T cells, they can be divided into subsets (Tc1 and Tc2) according to the cytokines they secrete. These subsets may differ in their capacity to kill and may even, in some cases, provide help for B cell antibody production or be involved in the induction of inflammatory responses. In addition, there is a host of cross-regulatory networks between different CD4⁺ and CD8⁺ subsets that control the magnitude and duration of immune responses. The observation that some antigens that are normally presented by MHC class II and seen by CD4⁺ T cells can be presented by MHC class I and stimulate CD8⁺ T cells increases the possibility for such interactions. During the next few years we can expect that our understanding of the biology of CD8⁺ T cells and their role in immunity will increase.