Recently, many investigators demonstrate that immunologic mechanisms seem to play an important role in the pathogenesis of Behcet's disease. The present study was undertaken to see the possible roles of NK cell activity in the pathogenesis of Behcet's disease and relationship among NK cell and T-cell and T-subsets. Authors evaluated NK cell activities in 14 patients and T cell, t-subsets in 7 patients. The results were as follows ; 1. The mean value of NK cell activities showed no statistically significant difference between patients group(57.1+15.8) and normal healthy control group(56.1+16.2). 2. The mean value of T cell(T), T-subsets(T,T)in 7 patients group 74.4+9.8, 41. 6+8.0, 24.4+10.1 showed no statistically significance compared with the mean value of normal healthy control group 67.5+4.3, 39.7+5.6,26.3+6.0 respectively. 3. The mean value of NK cell activities showed no statistically significant difference between 7 complete type patients' group(49.6+13.1) and 7 incomplete type patients' group(64.4+15.6)