The cell kinetic characteristics of 28 cases of oral leukoplakia were studied by in vitro double labelling with 3H-thymidine and autoradiography. As compared with normal oral mucosa, there were significantly higher LI, shortened Tc and increased labelled basal cells in the leukoplakia with epithelial dysplasia, and similar changes in LI, Tc and labelled basal cells were also found in several cases without epithelial dysplasia which were clinically homogeneous or evidently caused by tobacco use. The expansion of labelled cells was often found in the epithelium with shortened, even disappeared rete pegs. The significances of the findings described above was discussed. The authors consider cell kinetics study may be useful in monitoring the dangerous cases of leukoplakia.