In an attempt to interpret previous findings of a higher incidence of blood phenotype A and a lower incidence of blood phenotype O in patients with either obsessive-compulsive neurosis or hysteria, it was hypothesized that phenotype O might be associated with personality traits that render the individual less prone to developing neurotic symptoms. To test the validity of this hypothesis Form A of the Eysenck Personality Inventory was administered to 600 normal individuals and their ABO phenotype was determined. Our results failed to support the above hypothesis, because the blood phenotype of the participants did not differentiate them with respect to their mean neuroticism score. The possibility of an association between ABO blood phenotypes and other, more specific, personality traits, such as hysteroid or obsessional is presently under investigation.