A multicenter in-vitro study was conducted in 13 countries between May and November, 1992 to determine both the current bacterial epidemiology in Intensive Care and Hematology/Oncology units and the susceptibility of the organisms to cefpirome and other commonly used antibacterials. Eighty-nine hospitals each collected 100 consecutive nonduplicate aerobic clinical isolates from patients in either an Intensive Care (81%) or Hematology/Oncology (19%) unit. The major sources of isolates were respiratory, skin/wound, blood and urine. The MIC of eight different antibiotics was determined using a custom microdilution plate. Predominant bacteria accounting for 80% of the 8625 isolates included: staphylococci (26%); Escherichia coli (17%); Pseudomonas aeruginosa (12%); Klebsiella spp. (10%); Enterobacter spp. (8%) and enterococci (7%). Gram-positive isolates accounted for more than 35% of all isolates. Based on the susceptibility results to the predominant pathogens, the activity of the drugs tested could be categorized into three groups. Cefpirome and imipenem had the most potent in-vitro activity, followed by the third generation cephalosporins cefotaxime, ceftazidime and ceftriaxone, and then piperacillin. The large percentage of Gram-positive bacterial isolates in this patient population indicates the utility of antimicrobial agents that are equally effective against both Gram-positive and Gram-negative organisms.