Objective: To investigate the effects of 17β-estradiol (E2) levels onblood lymphocyte counts in women.Methods: Blood samples were obtained from 428 healthy women. Serum E2 levels were measured using the solid-phase enzyme-labelledchemiluminescent method. Complete blood count was performed bya fully automated cell counter. White blood cell differential, includinglymphocytes, was performed by volume, conductivity, and five-partscatter measurements (VCS technology). The participants were divided into four groups, according to the blood lymphocyte levels: <1000cells/µL (Group A), 1001–2000 cells/µL (Group B), 2001–3000 cells/µL(Group C), and 3001–4000 cells/µL (Group D).Results: The mean age of the participants was 37.03 years (between15 and 66 years). E2 levels on admission in the study group rangedfrom <11 to 4264 pg/mL, and the median E2 level was 121.98. Twelvewomen had high levels of E2, as a result of the ovulation inductiontreatment. Total lymphocyte count varied between 0.9×103 to as highas 105×103 cells/µL, and the median lymphocyte count was 2.6×103cells/µL. Lymphocyte–white blood cell ratio (LWR) was also studiedin addition to lymphocyte levels. The lowest LWR value was 9.1 andthe highest was 99.7. The medium E2 concentration was 40.3±11,114±144, 117.2±128, and 192.2±595 in Groups A–D, respectively. Therelationship between lymphocyte counts and LWR was positive, as expected. There were no statistically significant differences in lymphocyte counts either with age or E2 levels.Conclusion: It is well established that estrogens affect lymphocytefunctions in several ways. In the present study, we were unable todemonstrate a correlation between the E2 serum levels and bloodlymphocyte counts in women.