A number of studies show that only a few bacteria are dominating the infectious sinus diseases. In acute sinusitis hemophilus and pneumococci are prevalent. Recent results in chronic sinusitis indicate a greater importance of anaerobic bacteria. The bacteriological findings in sinusitis are influenced by many factors: 1. the sampling techniques (proof-puncture or nasal-swab); 2. transport time and transport medium; 3. bacteriological culture technique; 4. the isolated bacteria are not automatically pathogens. The difference between colonizing or contaminating bacteria and pathogenic bacteria should be taken into account. A lack of leukocytes, a mixture of bacteria and a viable count of 10(3) or lower indicates normal flora or contamination; 5. kind of infection: acut - chronic; dentogen - rhinogen; 6. mode and duration of therapy (antibiotics, surgery, irrigation); 7. age of patient, season of the year.