Infectious mononucleosis is a self-limiting lymphoproliferative disorder, which contribute to the development of the various clinical symptoms. Exudative tonsillitis was found to be caused by Epstein-Barr virus in 19% of all viral infections and may imitate a bacterial etiology. The aim of this study was to identify the microbes from the nasopharyngeal swabs obtained from the patients with exudative tonsillitis and to assess their susceptibility to antibiotics. The patients were hospitalized as an infectious mononucleosis after unsuccessful antibiotic therapy. 84 patients were investigated: group I--patients with serological positive infectious mononucleosis tests and group II--patients with acute exudative tonsillitis and with serologically excluded infectious mononucleosis. The diagnosis was confirmed clinically, haematologically, biochemically and serologically. Nasopharyngeal specimens were taken, once, at the first day of hospitalization. Then, routine microbiological assays were performed. Isolated strains were identified biochemically: API Strep, API Staph, API E, API Ne, APINH (bioMerieux). The susceptibility to antibiotics with an agar diffusion assay was performed according to Kirby-Bauer. We concluded that various, potentially pathogenic bacterial flora was found in throat during infectious mononucleosis. Haemophilus spp. and Staphylococcus aureus MSSA were isolated more frequently. Haemophilus influence was susceptible to cefotaxime and azytromycine. Candida albicans was isolated in every fourth patient. Streptococcus pyogenes as an etiological agent of exudative tonsillitis was confirmed in the group II. The pharyngeal candidiosis was also observed more frequently in the group II.