Using simple agglutination tests, ABO agglutinins were detected in a significantly higher proportion of the saliva from Othan B or A individuals. Anti-B was detected in a significantly higher proportion of the saliva from A, than Ai individuals. These observations and pedigree studies indicate that the ABO agglutinins in saliva may not be under simple genetic control. Low molecular weight serum antibodies probably traverse semi-permeable membranes appearing in the saliva.