The purpose of this study is to detect certain change in peripheral blood lymphocyte subpopulations in women with premature ovarian failure. The B cells, T cells and subsets were counted in 21 women with premature ovarian failure and 30 age-matched normal control women. The B cells were measured by identifying lymphocyte with surface membrane immunoglobulin and T cells and subsets by indirect immunofluorescence technique with the monoclonal antibodies OK T3, OK T4, and OK T8. The results were as follows. 1. No significant difference in the absolute number of B cells, T cells and subsets between women with premature ovarian failure and normal control women was observed. 2. The percentage of B cells, T cells and OK T8(+) cells in women with premature ovarian failure was not significantly different from that in normal control subjects respectively. 3. The percentage of OK T4(+) cells and OK T4/0K T8(+) ratio was significantly higher in women with premature ovarian failure than in control subjects.