A study performed at 12 hospitals in the Czech Republic in 2001 evaluated the Gram-negative bacterial pathogens most frequently associated with bloodstream infections and their susceptibility to a selection of antimicrobial agents. Of 831 Gram-negative strains, the most frequently isolated organisms were Escherichia coli (32%), Klebsiella pneumoniae (24%) and Pseudomonas aeruginosa (10%). E. coli isolates were relatively susceptible to the antibiotics tested, whereas K. pneumoniae were relatively resistant to all agents except meropenem, and P. aeruginosa to all agents except gentamicin and amikacin. Other agents showed variable rates of resistance to penicillins, third-generation cephalosporins, aminoglycosides and ciprofloxacin.