INTRODUCTION: Cell mediated immunity is important in host defense against viral infections and malignancies. Reactive lymphocyte is a non-malignant leukocytes that was found in the peripheral blood. It appears as a nonspecific response to stress. Today it is an atypical lymphocyte, Downey's cells, or reactive lymphocytes and is a marker of disease when it is found in the peripheral blood. Laboratory automation is increasingly developing in terms of hematology analyzers and algorithms in order to adequately detect abnormal patterns including reactive lymphocytes whose findings we really helpful in the diagnosis of the patient's condition. AIM OF RESEARCH: To determine the reliability of the findings of reactive lymphocytes in 60 patient samples. Of the total number of samples, 30 samples were related to healthy samples compared with 30 positive findings reactive lymphocytes. MATERIALS AND METHODS: Blood samples (n = 60) were used for the analysis were divided into two groups of 30 samples belonging to the healthy subjects with negative findings reactive lymphocytes. The remaining 30 samples belonged to subjects with positive findings reactive lymphocytes. The measuring instrument used for the purposes of analyzing is the hematology analyzer ADVIA 2120. As control was used microscopic examination of blood smears. RESULTS: Graphic display of Passing - Bablok regression was used to determine the reactive lymphocytes methods ADVIA-hem. analizator and microscopically for a group of healthy subjects. Results of regression results for the determination of reactive lymphocytes analyzer ADVIA and microscopic with 95% confidence with no significant deviation between the measured values. (Y = 1.000 +0.500 x) with P> 0.10. Graphic display of Passing - Bablok regression was used to determine the reactive lymphocytes methods ADVIA-hem. analizator and microscopically for a group of patients with pathophysiological changes. Results of regression results for the determination of reactive lymphocytes analyzer ADVIA and microscopic with 95% confidence with no significant deviation between the measured values. (Y = 1.300 +0.8083 x) with P> 0.10. CONCLUSION: 1. The reliability of the findings of the presence of reactive lymphocytes in hematology analyzer ADVIA 120 is confirmed reproducibility-checking the accuracy of a single sample repeated 10 times with CV = 4.5%. 2. Acceptable level of comparability share (percentage) of reactive lymphocytes specific to the hematology analyzer and examination of smears stained using MGG is determined because with 95% confidence there are no significant differences in the results in a group of healthy subjects. 3. Acceptable level of comparability share (percentage) of reactive lymphocytes specific to the hematology analyzer and examination of smears stained using MGG is determined because with 95% confidence there are no significant differences in the results in the group of patients with pathophysiological changes. 4. The level of sensitivity (the lowest number of reactive cells) is determined by analyzer which classifies the value of 1%. This value is rounded because the classification of the analyzer expressed as a percentage of the value to one decimal place which should be taken into account when interpreting the results.