For the first time, clinical microbiologists have the option of purchasing or leasing a variety of automated blood culture systems. Although the performance characteristics of the BACTEC radiometric and nonradiometric blood culture systems are well-documented, we are only beginning to learn the performance characteristics of CMBCS. Well-designed and executed controlled clinical trials are needed to establish performance characteristics and to address issues that are unique to CMBCS. In particular, controlled clinical comparisons of different CMBCS are needed. In terms of the impact on clinical microbiology laboratories, there are no published data to support claims that the use of these systems decreases laboratory workload, staffing, or costs. Although such an impact seems reasonable and even likely, unequivocal documentation of such savings would make it easier for many laboratorians to justify the cost of purchasing or leasing one of these systems. Similarly, there are no published data regarding the long-term reliability of these systems while in clinical use. A documented track record of mechanical and electrical reliability would be useful to clinical microbiologists contemplating the acquisition of a new blood culture system.