In order to determine the recent trend of anaerobic bacteria isolation and the susceptibility of Bacteroides to antimicrobial agents, an analysis was made on the data of routine anaerobic cultures at Yonsei Medical Center during the period of September 1980 to August 1981. The following results were obtained. 1) A total of 336 isolates of anaerobic bacteria were obtained from various clinical specimens. Among the isolates 38.7% were gram-positive cocci and 53.3% were gram-negative bacilli. 2) Peptococcus magnus(20.3%) and P. asaccharolyticu(16.5%) were the frequently isolated gram-positive cocci and B. fragilis(70.4%) and B. thetaiotaomicron(15.1%) were the frequently isolated gram-negative bacilli. 3) Anaerobic bacteria were frequently isolated from specimens of abdomen and female genital tract. Peritonitis and intra-abdominal abscess were frequent clinical findings. 4) Among the anaerobe positive specimens, 22.4% yielded anaerobes alone while the remaining 77.6% also yielded aerobic bacteria. 5) Most of the B. fragilis and B. thetaiotaomicron isolates were susceptible to cefoxitin and chloramphenicol, but resistant to tetracycline.