The purpose of this study was to investigate a possibility of chronic or intermittent bacteremia in patients undergoing orthodontic treatment with fixed orthodontic appliance. Orthodontic patients who had been injured by orthodontic appliances and/or suffered from gingivitis were selected. They had not taken any antibiotics for 1 month. The number of subjects were 21 including 7 males and 14 females. Blood samples of the subjects were cultured and, IgG, IgA and IgM levels in the serum were quantified. The author found following results. 1. No bacterial growth was found in 7-day culture of all the samples. 2. The immunoglobulin levels in serum were confined in normal range. 3. This study could not deny the possibility of transient bacteremia episode undergoing orthodontic treatment.