Roland, Fredy P.: Interaction of blood with Enterobacteriaceae. Hemolysis, hemagglutination, fibrinolysis. Am J Clin Pathol 67: 260–263, 1977. One thousand eighty enterobacteriaceae, isolated during a period of three months, were tested for the presence of hemolysis, hemagglutination and fibrinolysis on human erythrocytes and plasma. The Escherichia coli have the greatest diversity of action on the blood. Of 481 strains, 32.9% were hemolytic, 21.9% fibrinolytic, and 10.5% hemagglutinating. Of 190 strains of Klebsiella, 95.2% were fibrinolytic. Of 53 strains of Enterobacter, 90.6% were fibrinolytic, and of 53 strains of Enterobacter hafniae, 66% were fibrinolytic. Of seven strains of Serratia, 28.5% were hemolytic and 14.3% fibrinolytic. The Proteae were mostly fibrinolytic: 60.5% of 141 strains, with three strains being hemolytic and fibrinolytic. Of 19 strains of Citrobacter, 52.6% were fibrinolytic only. Providencia, Salmonella and Shigella did not interact with human blood. The patterns of blood interactions with the different species of Enterobacteriaceae are of value in the evaluation of the pathogenesis of the infections and septicemias they cause. Their study is an essential step in the understanding of the sequence of events leading to severe disturbances of the blood-clotting mechanism.