Abstract
The classic iris lesion in a patient with erythema multiforme bullosum were reproduced grossly and microscopically by the intradermal injection of a variety of heat-killed, gram-negative bacteria and their common endotoxin, lipopolysaccharide [LPS] W. In vitro exposure of the patient''s blood to these antigens induced specific fibrin microclots characteristic of a hypersensitivity state. Some cases of erythema multiforme associated with a variety of respiratory, gastrointestinal or urinary tract infections may represent a single specific delayed sensitivity reaction to the bacterial LPS.