Pseudomonas aeruginosa produces a large number of extracellular toxins, which include phytotoxic factor, pigments, hydrocyanic acid, proteolytic enzymes, phospholipase, enterotoxin, exotoxin, and slime. The most important factor in the pathogenicity of P. aeruginosa is the elaboration of a group of protein exotoxins. These exotoxins can produce leukopenia, acidosis, circulatory collapse, necrosis of liver, pulmonary edema, hemorrhage, and tubular necrosis of kidneys. Passive administration of antitoxic sera against these exotoxins is able to protect against lethal infections with P. aeruginosa in the absence of antibody against the cellular antigens. The proteolytic enzymes produced by P. aeruginosa are responsible for the hemorrhagic and necrotic changes in the skin, as well as destruction of the cornea in eye infections. Phospholipase may be responsible for destruction of pulmonary surfactant with resultant atelectasis. This effect, together with the necrosis of lung tissue, may be important in the pathogenesis of the damage to lungs in the patients with pneumonia due to Pseudomonas. Strains of P. aeruginosa are capable of producing an enterotoxin that is probably responsible for diarrheal diseases.