A chronic paranasal sinusitis is a very common disease in the Otorhinolaryngological field. There are many articles reported about the bacteriological studies on the chronic maxillary sinusitis. It seems to be important to check periodically the changing pattern of pathogenic organisms and their sensitivity to antibiotics. The authors performed a bacteriological study in 167 maxillary sinuses of 130 patients of chronic maxillary sinusitis. All bacterial specimens were obtained by antral puncture, intranasal antrostomy or Caldwell-Luc's operation. The following results were obtained: 1) Organisms were isolated from 125 cases (74.9%) of 167 sinus cultures and 42 cases (25.1%) of 167 sinuses were sterile. 2) Monomicrobial infection was found in 100 cases (80%) and mixed infection was found in 25 cases (20%). 3) Among 150 strains, the most frequently encountered organism was staphylococcus in 53 strains (35.3%) and 36 strains of streptococcus pneumoniae (24%), 32 strains of hemolytic streptococcus (21.3%) and 29 strains of the others (19.4%) were isolated in order. 4) Staphylococcus strains were sensitive to novobiocin, cleocin, amikacin, geopen and cephalothin. 5) Streptococcus pneumoniae strains were sensitive to geopen, cephalothin, penicillin and erythromycin. 6) Hemolytic streptococcus strains were sensitive to novobiocin, penicillin and erythromycin.