Evaluation of different types of lymphocyte subpopulations in the peripheral blood has unknown and controversial significance in diagnosis of infertility. The aim of the study was to evaluate selected blood lymphocytes in patients treated with intracytoplasmic sperm injection (ICSI).<br /><br /><strong>MATERIALS AND METHODS</strong><br />women were divided into three groups: (1) control fertile group (n=18), (2) infertile women that achieved (n=32), and (3) did not achieve a pregnancy after ICSI (n=26). The following types of leukocytes were analyzed by three-colour flow cytometry by detection of specific CD antigens: lymphocytes T (CD3+), B (CD19+ and CD5+CD19+), T and B (CD5+), NK cells (CD56+CD16-, CD56-CD16+, CD56+CD16+, CD56brightCD16-, CD56dimCD16+). Additionally, the antigen of early activation (CD69) was evaluated on T, B and NK cells. The results were presented as a percentage and total counts of all lymphocytes.<br /><br /><strong>RESULTS</strong><br />The percentage of total NK cells (CD56+CD16+, CD56+CD16- and CD56-CD16+) did not differ between pregnant and non pregnant women and was lower comparing to control group. Fractions of CD56-CD16+ cells were higher in pregnant vs. non-pregnant women. The percentages of CD56brightCD16- NK cells were higher in control group comparing to both ICSI treated groups. Other fractions of lymphocyte subpopulations, including activated cells (with CD69 expression) did not differ between the analyzed groups. Total counts of CD56-CD16+ cells were higher in pregnant vs. non-pregnant group, and the CD56brightCD16- cells was more abundant in control group vs. women with unsuccessful ICSI.<br /><br /><strong>CONCLUSIONS</strong><br />Testing of peripheral blood NK cells and the others lymphocytes has limited value as a prognostic factor in ICSI treated patients. The antigen of early lymphocytic activation (CD69) has not any predictive value in prognosis of ICSI outcome.<br /><br />