The past year has seen the first direct evidence that parasite-specific CD8+ T cells can protect cattle against patent infection with Theileria parva. These studies were based on the adoptive transfer between monozygous twins of lymphocytes responding to a challenge with the parasite. Immunization trials are also continuing with a candidate neutralizing vaccine based on the dominant antigen of the T. parva sporozoite surface. This progress has considerably enhanced the prospects for an improved vaccine against the parasite.