Pseudomonas aeruginosa, an organism ubiquitous in nature, has assumed an increasingly prominent role as the aetiological agent in serious infections in hospitalized patients. Pseudomonas has a number of pathogenic properties, which include its capsule, exotoxin A and various proteases. Although normal individuals infrequently carry this organism as part of their flora, patients with burns, malignancy, and after surgery often are colonized and subsequently infected with Pseudomonas. Infections produced by Pseudomonas include bacteraemia, respiratory infection, urinary tract infection, osteomyelitis, and infections of burns and soft tissues. Because of the resistance properties of Pseudomonas, therapy has been difficult. However, the development of highly effective antipseudomonas penicillins has brightened the picture. Nonetheless great progress can still be made in control and prevention of serious Pseudomonas infection.