Abstract: The T-cell subsets and NIA cell activity of peripheral blood lymphocytes in patients with ohronioity atrophic gastritis(CAG) or gastric cancer(GC) were tested.In the rosette formation assay,OKT.monoclonal antibody sensitized sheep reel blood cells were used to detect T-cell subsets. The MTT orrimetric assay w as used to detect N K cell activity .Significant impairment of NK cell activity, a decreased rate of CD⁺₃cell, an increased rate of CD⁺₈ cell and a declined CD₄/CD₈ ratio were noted in CAG patients，compared with normal subjects.In GC patients before operation, NIA cell activity,CD⁺₃，CD⁺₄and CD⁺₈、cell rate and CD₄/CD₈ cell ratio all decreased significantly as compared with normal subjects. In comparing CAG patients with GC patients before operation, NK cell activity was impaired, CD⁺₃ cell rate increased, CD⁺₈ cell rate decreased, CD₄/CD₈ cell ratio declined. However two weeks after operatic n, CD⁺₃cell rate, CD⁺₄cell rate, CD⁺₈cell rate and CD₄/CD₈ cell ratio were all recovered. In conclusion, the function of cell-mediated immunity in CAG patients was disturbed and in GC patients the disturhance was more severe than in CAG patients. Two week after operation, the function of cell-mediated immunity in GC patientswas recovered.