Tests for a range of autoantibodies, and counts of lymphocytes, B cells, T cells, and T cell subsets were performed in 45 Chinese patients with premature ovarian failure and 45 age-matched normal control subjects. Eight patients (18%) were positive for at least one autoantibody. Only one patient was positive for antiovarian antibody. Patients with autoantibodies had a significantly higher percentage of circulating B cells. The lymphocyte, T cell, CD4+, and CD8+ counts in patients with premature ovarian failure were significantly higher than those in the control group, but the CD4:CD8 ratio was significantly lower in women with premature ovarian failure. There was a significant negative correlation between plasma estradiol levels and CD8+ counts, and a significant positive correlation between plasma estradiol levels and CD4:CD8 ratios. The changes in lymphocytes and lymphocyte subpopulations in premature ovarian failure may be due to estrogen deficiency.