We compared the BACTEC Plus 26/27 culture system (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) with and without fastidious organism supplement with conventional centrifugation preparation and plating for the recovery and speed of detection of microorganisms. A total of 1,101 sterile body fluid specimens were collected and processed at five hospital laboratories, yielding 234 (21%) positive cultures. Of the 176 isolates considered clinically significant, 133 (76%) were recovered by both the BACTEC system and conventional culture, while 28 (16% [P < 0.005]) were recovered by BACTEC only and 11 (6%) were recovered by conventional culture alone. There were no statistically significant differences in the speed of detection of microbial growth. It was found that BACTEC, with or without the addition of fastidious organism supplement, exhibited improved sensitivity for the recovery of microorganisms, including fastidious bacteria.