The protozoan parasite Theileria parva infects and transforms T and B lymphocytes and causes acute, often fatal disease. Cattle can be immunised against the parasite employing an infection and treatment protocol, but although this vaccination method has been used successfully in the field, it is difficult to apply on a large scale. This has led to efforts to develop alternative vaccines. Infected lymphoblasts express high levels of class I and class II MHC proteins on their surface and immune cattle mount strong CD4 and CD8 T cell responses directed against the parasitised cells. Adoptive transfer studies have shown that parasite-specific CD8 T cells are key mediators of immunity. In this presentation, I will outline new strategies we have used to identify antigens recognised by parasite- specific CD8 and CD4 T cells, including the development of high throughput methods to allow rapid definition of bovine MHC genotypes, to characterise peptides eluted from cell surface class I MHC proteins and to examine antigenic diversity in field parasite populations. Data on the intracellular pathways involved in processing of parasite antigens within parasite-infected cells, which indicate that antigens recognised by both CD4 and CD8 T cells are processed via a proteasome-dependent pathway, will also be presented. The implications of the findings from these studies for vaccination will be considered in relation to current efforts to develop subunit vaccines.