To assess the prevalence of antimicrobial-resistant pathogens among the most common bloodstream isolates, we examined antimicrobial susceptibility data from The Surveillance Network Database-USA, an electronic surveillance system that collects data from 118 clinical microbiology laboratories across the United States. Between 1995 and 1997, resistance to both vancomycin and ampicillin was much more prevalent among Enterococcus faecium than Enterococcus faecalis, suggesting the need for laboratories to identify to species. When staphylococcal isolates were examined for reduced susceptibility to vancomycin (minimum inhibitory concentration = 4 microg/mL), the frequency was highest in methicillin-resistant coagulase-negative staphylococci. We also learned that nonsusceptibility to ceftazidime in Klebsiella pneumoniae was more prevalent among isolates from blood (12.7%) than among isolates from urine (7.1%) or respiratory sources (9.3%). Although antimicrobial resistance is low overall for isolates of Escherichia coli from blood, the prevalence of cefoxitin resistance among ceftazidime-resistant strains (61.9%) suggests the action of mechanisms other than extended-spectrum beta-lactamase.