Abstract: To investigate the Natural Killer （NK） cell activity of peripheral blood in the end-stage renal disease renal disease （ESRD） patients, a flow cytometry assay based on the cytotoxic action on target cells was performed for specimen obtaind from 13 cases on chronic hemodialysis. The result showed a marked decrement of NK cell activity in these patients as compared with the control （12.36 ± 5.09 vs 17.84 ± 3.71 P＜0.001）. The response of NK cell in this group of patients to IL-2 stimulation was also measured. Obviously, in normal control there was an increase of cytotoxic action of these cells after the addition of IL-2 into the culture media. Yet it was not present in the ESRD. It indicated that both the activity of NK cell and their response to IL-2 were attenuated markedly in ESRD, which is in accordance with the high susceptibility to malignancy and infection of these patients. Recently, NK cell can also be recognized by its surface antigen CD16（Leull）. Using FITC Labelled anti CD16 McAb and flow cytometry technique, we enumerated the number of NK cell in the specimen from this group of patients. The results were comparable to that assessed by the NK cell activity as outlined in this paper.