Abstract We have used the monoclonal antibodies IL-A111, CACT116A, to investigate the expression of interleukin 2 receptors (IL-2R) by ovine peripheral blood T cells. Monoclonal antibodies (mAbs) IL-A111 and CACT116A reacted with concanavalin A (Con A) activated ovine lymphocytes and both mAbs did so with similar FACS (fluorescence activated cell sorting) profiles and fluorescence intensity. Following activation by Con A all three major ovine T cell subsets, namely CD4 +, CD8 + and γ/δ T cells, express the IL-2R. All γ/δ T cells express IL-2R within 12 h following activation by Con A in vitro whereas α/β T cells do not express the IL-2R until 24 h after the start of culture with the mitogen. In freshly isolated peripheral blood a small percentage of lymphocytes, which are almost all CD4 +, express the IL-2R.