The relation of ABO blood types to obsessional personality traits, as measured by the Leyton Obsessional Inventory (LOI), was studied in a sample of 600 normal individuals. High scorers of the LOI trait portion demonstrated a significantly lower incidence of phenotype 0 and a significantly higher incidence of phenotypes AB, A and B, taken together, compared to those of a general population sample and the entire study group. Findings of the present study, in conjunction with previous findings concerning a lower incidence of phenotype 0 and a higher incidence of phenotype A in obsessive compulsive patients, could be interpreted as indicating that phenotype·may be associated with personality traits hindering the development of obsessive-compulsive symptomatology