A microculture technique for the mixed lymphocyte culture test(MLC) in the sheep is described. The optimal incubation periods for the MLC are varied from 4 to 6 days depending on the sources of lymphocytes. It is found that a 2.5:1 stimulator-responder cell ratio and the responder cell concentration of $1{ imes}10^5$ cells/well produce the highest($^3H$)-thymidine incorporation. Moreover cryopreservation of bovine lymphocytes results in satisfactory and reproducible MLC reaction. It is also evident that the MLC reactions of the sheep are under the control of histocompatibility matching between the stimulator cells and the responder cells. Significance of the technique as a too! for study on cell mediated immunity in sheep system, either normal or squamous cell carcinoma-bearing, are discussed.