The emergence of multi-resistant Gram-negative bacteria has created a most alarming clinical situation. The armamentarium of antibiotics used against this group of organisms is rapidly being depleted. Our routine therapeutic approach to control and prevent these Gram-negative bacteria from gaining a foothold was the empirical use of an aminoglycoside combined with piperacillin. However, aminoglycoside resistance is now routine rather than unusual. We evaluated the role of the monobactam aztreonam in burn wound infections and compared it to the aminoglycosides amikacin and gentamicin as well as piperacillin for the Enterobacteriacae and Pseudomonas aeruginosa. A total of 1274 Gram-negative isolates including P. aeruginosa were evaluated for susceptibility to the above-mentioned antibiotics from January 1995 to August 1995 (Table I). Among the Enterobacteriacae, aztreonam was more effective than amikacin and piperacillin (58.4 per cent vs. 45.8 per cent, respectively). However, it still fluctuated among the Enterobacteriacae as did the aminoglycosides. One major significant finding was that while susceptibility to aztreonam was variable for the Enterobacteriacae, P. aeruginosa remained 90 per cent susceptible to aztreonam and 90 per cent susceptible to piperacillin, whereas it was 79 per cent resistant to the aminoglycosides. Consequently, when choosing an antimicrobial in a suspected P. aeruginosa burn wound infection, aztreonam and piperacillin should be considered as the first line of defense.