Aztreonam, the first monobactam, has been used extensively in the treatment of a variety of infections caused by gram-negative pathogens. It has been shown to be highly effective against susceptible bacteria without causing serious adverse reactions. Its pharmacologic profile can be attributed to its unique chemical properties and mechanisms of action, which differ substantially from those of the bicyclic beta-lactams, such as the penicillins and cephalosporins. Administered parenterally, aztreonam provides peak serum concentrations for most Enterobacteriaceae and Pseudomonas aeruginosa. It is widely distributed throughout the body. Excretion is largely dependent on renal mechanisms, so dosage can be adjusted in the presence of renal impairment. The clinical uses of aztreonam include treatment of urinary tract, lower respiratory tract, and intraabdominal infections, as well as septicemia, endometritis, pelvic cellulitis, and skin and skin structure infections due to aerobic gram-negative organisms. It is concluded that aztreonam can be used with confidence in the single-drug treatment of susceptible aerobic, gram-negative pathogens. In the treatment of mixed infections, or those of unknown etiology, however, combination therapy is recommended to ensure coverage of gram-positive and anaerobic bacteria.