In this thesis, the expression of the WC1 protein on ovine γδ T cells was analysed. A large number of monoclonal antibodies exist which recognise epitopes of this molecule in the bovine species. Their reactivity with ovine WC1 protein was examined, both at a cellular level and protein level. The results in this thesis, along with those published by others during the course of the thesis, identified WC1 as a protein complex with great diversity at the genetic level, and possibly at the post-transcriptional or post-translational level. Work in this thesis also confirmed that, with respect to the expression of WC1 proteins, γδ T cell immunochemistry in the ovine species is similar in some, but not all, respects to that seen in the bovine species. γδ T cells are more prevalent in the ovine species than in either the human or murine species. This may imply that sheep have a greater requirement for γδ T cells than either the human or murine species. The in vitro activation and proliferative response of ovine γδ T cells, following in vitro culture with mitogen or antigen, was examined and compared to the responses of ovine αβ T cells. The responses by γδ T cells to both antigen and mitogen were different to the responses by αβ T cells. All γδ T cells expressed markers of activation within 8hrs of culture with mitogen, in contrast, it took 24hrs for all αβ T cells to express the same markers. In addition, all γδ T cells expressed markers of activation following culture with antigen whereas there was little change in the expression of these markers on αβ T cells. Purified γδ T cells proliferated following culture with mitogen but did not proliferate in response to culture with antigen. In addition, purified γδ T cells did not proliferate following culture with allogeneic lymphocytes. These results implied that the function of γδ T cells within the immune system may be markedly different to the function of αβ T cells.