Bacteremia due to Mycobacterium abscessus, a rapid grower, belonging to the Runyon group IV, occurred in an inpatient with fever of unidentified origin in Shinshu University Hospital. To the best of our knowledge, this is the first documented case of M. abscessus bacteremia in Japan. The organism initially grew on Sheep blood agar plates after terminal-subculturing from the BacT/Alert SA aerobic blood culture bottles with no positive signal, and was subsequently identified as M. abscessus using 16S rRNA sequence analysis. We evaluated the BacT/Alert SA bottles for the detection of Mycobacterium species, with special reference to the rapid growers including M. abscessus by seeding experiments and obtained the following findings: 1) The BacT/Alert system shows the positive sign when the bacterial cell counts reach around 10(6) to 10(7) CFU/ml. 2) The System requires around 6 to 7 days of incubation to obtain a sufficient bacterial growth for the positive signal. 3) The System may result in false negative under the 5-day-culture method recommended by American Society for Microbiology in cases of using automated blood culture systems. 4) So-called the blind- or terminal-subcultures from the bottles are inevitable to perform for precluding the false negative cases.