The presence of antimicrobial agents in patients' blood is thought to represent an important source of false-negative blood cultures. This has led to the incorporation of agents with inhibitory effects on antimicrobial drugs into culture medium. In the present study, Bactec aerobic resin-containing blood culture medium was compared with Bactec hypertonic blood culture medium. 504 patients receiving cytostatic and/or antibiotic treatment were studied. Sensitivity calculations on detection of bacteremia in these patients gave 0.91 for the resin medium and 0.79 for the hypertonic blood culture system and showed a significant difference (p = 0.016). In addition, the resin-containing system more rapidly detected positive cultures than the hypertonic system.