The two stage freezing technique was adapted for use with sheep lymphocytes. Parameters investigated were lymphocyte concentration, composition of thawing medium and DMSO concentration. The main difference between this and earlier published techniques is the use of a high DMSO concentration (17%). The technique adopted was both simple and reliable. It consistently gave lymphocyte viabilities of 95% or more in thawed cell suspensions. The procedure is apparently without effect on lymphocyte antigen expression and thus appears very suitable for use in microlymphocytotoxicity tests.