Chronic paranasal sinusitis is one of the most common diseases in the otolaryngological field. Among many therapeutic modalities, antibiotic therapy is the most important part. In selecting antibiotics, there must be cultures and isolation of the etiologic microorganism, and the tests identifying the sensitivity and the resistance to the various kind of antibiotics. The authors cultured secretion of sinuses from 44 patients, isolated the microorganisms and examined the susceptibility to antibiotics. The results were as follows : 1) Among 44 patients, microorganisms were isolated in 14 patients(32%). 2) Six of the isolates of bacteria were coagulase positive staphylococcus(40%), 4 were coagulase negative staphylococcus(27%), and 3 were α-hemolytic streptococcus(20%). 3) In purulent sinus secretion, the positive culture rate was 46%(11 of 24 cases), but 15%(3 of 20 cases) in mucoid secretion. 4) In patients not receiving antibiotic therapy, there was isolation of strains in 12 of 29 cases(43%), and in those of receiving antibiotic therapy, 4 of 15 cases(27%). 5) In 7 cases the chronic maxillary sinusitis was associated with hypertrophy of tonsils and adenoid, and the sinus secretion was mucoid and sterile in all the cases. 6) The isolated strains were susceptible to cefoperazone, cefoxitin and carbenicillin, but resistant to kanamycin, gentamicin, and pencillin.