Wistaria floribunda agglutinin (WFA), Sophora japonica agglutinin (SJA) and Maclura pomifera lectin (MPL) were employed as immunofluorescent and leucoagglutinating reagents to study murine lymphocytes. WFA, which labels 90% of thymocytes, binds to only 57% of the splenocyte population. The latter subset corresponds to surface immunoglobulin bearing cells. Differential agglutination of splenocytes with this lectin results in the isolation of a WFA negative population which exhibits T-lymphocyte surface markers. The agglutinable splenocytes bind only 2.5 times more WFA than non-agglutinable cells suggesting that the preferential agglutination of B-splenocytes is due to a combination of reduced cell surface negative charge and increased number of lectin binding sites on these cells as compared to T-lymphocytes. Forty percent of splenocytes are positive for SJA and differential agglutination of splenocytes yields a population of SJA non-agglutinable cells that are not labeled by this lectin. The two populations fractionated by SJA are unrelated to T- and B-lymphocyte subsets. Differential agglutination of thymocytes by SJA yields a non-agglutinable group representing 42% of total thymocytes. Although the nature of the two thymocyte subsets discriminated by SJA remains unknown, this lectin appears useful in identifying and separating unique thymocyte and splenocyte populations.