A total of 1,592 blood cultures without macroscopic signs of bacterial growth in the first 12-24 h of incubation were processed for both acridine orange stain and blind subculture. One hundred and twenty-one (7.6%) blood cultures were positive by either method; of these, 105 (8.68%) were positive by both methods, 11 (9.1%) positive by acridine orange and negative by subculture, and 5 (4.1%) negative by acridine orange and positive by subculture. The difference between the 116 blood cultures positive by acridine orange and the 110 blood cultures positive by subculture was not statistically significant (p greater than 0.1). Gram stain performed on all acridine orange positive cultures failed to reveal bacteria in 14 cases. Acridine orange staining is a sensitive, rapid and reliable method for detecting bacteria in blood cultures early during incubation. The method is inexpensive and easy to perform and can be substituted for blind subcultures.