1. Saline suspensions of human red cells, as well as those of several animal species, were agglutinated by normal saline extracts of the Fava bean.
2. This agglutination was potentiated in titer 100-fold in a medium of 10 per cent acacia, as a diluent.
3. The inhibition of the hemagglutination action of the Fava bean extract by human serum was apparently attributable to the gamma globulin fraction.
4. The Fava bean principle could be transferred from cell to cell, as shown by heat-elution and acacia technics.
5. Fava-sensitized red cells did not exhibit increased susceptibility in the test tube to complement, hemolysin, or osmotic or mechanical fragility.
6. The mechanism of in vivo red cell destruction in Favism is as yet unknown, but a special immunologic susceptibility to the action of the bean’s principle is suspected in certain persons.
7. It is suggested that the relation of acacia to Fava-sensitized red cells may form the basis of a diagnostic test for Favism in the early, acute stages of the disease.