In this study we examined bovine MHC class I genes using both molecular and cellular approaches. There is evidence for the existence of five or six classical class I loci in cattle, with the number of genes expressed varying between haplotypes. Most alleles are putatively assigned to a locus according to their grouping following phylogenetic analysis. Here we applied reference strand mediated conformational analysis (RSCA), a high resolution typing method, to four of these groups: 1, 2, 3 and 6.  Using group-specific primers and two reference strands 22 potential new alleles were identified with one probable pseudoallele in group 1. Based on the results obtained, and previous phylogenetic analysis, groups 1 and 3 appear to be the most polymorphic. The need for a reliable typing method for MHC class I genes in cattle can be seen through studies of CD8+ T cell responses to Theileria parva. T. parva is an intracellular parasite against which CD8+ CTL have been shown to be the principal effector cells in infected cattle. Previous studies identified a clear bias in class I restriction of CTL to either the maternal or paternal haplotype, and showed that haplotypes differ in their ability to restrict this response. We have extended these studies using animals with well-characterised haplotypes. We showed that the A14 haplotype is dominant over A10, and A18 is dominant over A31. A14 expresses three class I genes, D18.1, D18.4 and D18.5. No significant difference in levels of killing against D18.1 or D18.4 targets was observed indicating that D18.5 may be the dominant gene on this haplotype.