Aztreonam is the first synthetic monobactam used in practical medicine. It is effective in Gram-negative aerobe infections. It inhibits the growth of most Enterobacteriaceae in concentrations below 2 mg/ml, and of Pseudomonas aeruginosa below 16 mg/ml. It shows a widespread, distribution achieving effective therapeutic concentration there, where infections are seen most frequently. The half-life is from 1.6 to 2.0 hours. It can be administered to patients every 8 and 12 hours in single parenteral doses of 0.5, 1.0, and 2.0 g. Aztreonam is a non-toxic antibiotic, a weak hapten with slight allergenicity. It has found therapeutic use together with the antibiotics directed against aerobic and anaerobic bacterial Gram-positive flora, and it is used in the therapy directed against infections with Gram-negative aerobes. It is an effective antibiotic in nosocomial infections, in oncological patients with neutropenia, and in elderly patients.