The occurrence of bacteremia was investigated in 39 patients undergoing tooth extraction (Group 1), surgical removal of impacted third molars (Group 2), or removal of osteosynthesis plates (Group 3). None of the 39 patients had bacteremia before anesthesia or after nasal intubation for general anesthesia. In two of 23 patients bacteria could be isolated after local anesthesia. Microorganisms were isolated in 14 of 19 patients (74%) with tooth extraction. In nine, a mixture of facultative anaerobic ("aerobic") and strict anaerobic bacteria were identified; in five, anaerobes were isolated exclusively. Two to 130 bacteria were cultured per 10 ml venous blood. Endocarditis causing alpha-hemolytic streptococci were found in seven cases (50%). At least one of the predominating anaerobes (Bacteroides, Fusobacteria, or Peptostreptococci) were found in all positive cases. Bacteremia was found in 40% of the Group 2 patients. There was no bacteremia in the Group 3 patients. The pathogenic relevance of anaerobic bacteremia is discussed and as a consequence it is suggested that the risk of developing organ abscesses as well as the problem of endocarditis following dental bacteremia has to be taken into consideration. On the basis of sensitivity testing, erythromycin does not appear to be the drug of choice in penicillin-allergic patients.