Backgrounnd/Aim. Study of the association between Epstein-Barr virus (EBV) and the tumors of the nasopharynx renders an opportunity to introduce causal treatment. Already have been proven the anti-EBV (anti-Epstein-Barr nucleus antigene) antibodies in the blood serum of the patients infected with EBV, while over 91% of the patients with nasopharyngeal malignant tumors also have a detectable anti-EBV marker. The aim of this research was to determine if there were anti-EBV antibodies in the serum of the patients with the already verified nasopharyngeal malignant tumors, and, if there were, to determine the quantitative ratio to the values in the serum of the healthy controls. Methods. The study involved 74 individuals in the period from 1994−2001 divided into four groups: group A counting 11 patients with undifferentiated carcinome of nasopharyngeal type (UCNT); group B counting 25 patients with UCNT Xray treated at least three years before the onset of the study; group C including 28 healthy subjecets (blood donors), and the group D with 10 patients with planocellular nasopharyngeal carcinoma. Serologic diagnostics of the patients serum was performed using the techniques of Reedman and Klein for the detection of anti-EBV antibodies in the serum. Results. The presence of the statistically significantly higher values of the mean geometric titer (MGT) of the anti- EBNA antibodies was determined in 36 patients with histologically verified UCNT as compared with the control groups including 10 patients with planocellular carcinomas of the nasopharynx and 28 blood donors. Presented were anti-EBNA titers with 95% confidence interval for any participants according to the Hoo clinical classification of nasopharyngeal tumors, as well as according to the fact if they had been radiotreated within the previous three years. Conclusion. The results of this study confirm the conclusions of the recent literature on the possible etiopathogenesis of nasopharyngeal tumors and the use of viral anti-EBNA antibodies as viral markers in the diagnostics of UCNT diseases. .