To describe the emperipolesis of lymphocytes and investigate the factors affecting lymphocyte emperipolesis in the KB cells and the relation of the emperipolesis to the biological behaviors of the lymphocytes.After pre-stimulation with phytohemagglutinin (PHA), interleukin (IL)-2, a-CD3, and PHA+IL-2, respectively, the peripheral blood lymphocytes (PBLs) isolated from healthy donors were mixed with KB cells to observe the emperipolesis of the PBLs under inverted microscope every other hour, and calculate the tumor-adhesion/emperipolesis indices of the PBLs. The cell mixture was then fixed with cool acetone and stained by Giemasa to observe emperipolesis between PBLs and KB cells. The occurrence and development of emperipolesis between PBLs and KB cells was also observed under scanning electron microscope (SEM) at 1, 2, 4, and 6 hours after fixation.The tumor-adhesion/emperipolesis indices of pre-stimulated PBLs were significantly higher than those of non-stimulated PBLs, and the indices of PHA+IL-2 group were the highest. The PBLs underwent morphological changes in the course of PBL emperipolesis mixed with KB cells as observed under SEM.Pre-stimulation can enhance the tumor-adhesion/emperipolesis indices of the PBLs. The emperipolesis might be a means of cytotoxicity of the PBLs.