The purpose of this study was to determine whether the BACTEC NR-16A and NR-17A media were more effective than the BACTEC NR-6A and NR-7A media in recovering organisms from the blood of patients undergoing antimicrobial therapy. A total of 986 sets of four blood culture bottles were compared, giving 141, 174, 93, and 104 isolates with BACTEC NR-6A, NR-16A, NR-7A, and NR-17A, respectively. BACTEC NR-6A and NR-7A media recovered 234 isolates, whereas BACTEC NR-16A and NR-17A media recovered 278 isolates. The recovery rate of bacteria when aerobic resin media were used was better than that with conventional aerobic media (P less than 0.001). The mean detection times were 51.5 and 69.7 h with NR-16A and NR-6A, respectively (P less than 0.01), whereas they were 68.2 and 71.3 h with NR-17A and NR-7A, respectively (P greater than 0.05). The small number of anaerobes recovered precluded a statistical comparison of relative recovery for that group of organisms.