To date, clinical use of aztreonam has been remarkably restrained and widespread enthusiasm for addition to hospital formularies similarly moderate. Its most accepted indication appears to be in gram-negative bacillary infections in the penicillin-allergic individual where one might ordinarily use an extended spectrum penicillin or a third generation cephalosporin. In all individuals its clinical efficacy appears similar to that of the aminoglycosides, not clinically superior but offering a higher therapeutic index by virtue of its lack of nephrotoxicity and ototoxicity. Its second application, therefore, is as an aminoglycoside-sparing agent even for multiresistant gram-negative bacillary infections, and although by no means inexpensive it offers an efficacious and safe alternative to aminoglycosides in the elderly and other patients with renal insufficiency. Aztreonam can be used effectively in combination with non-beta-lactam agents for mixed infections, even though it is not synergistic in vitro with vancomycin and clindamycin.