First example of By phenotype.

In ABO blood grouping red cells of a young healthy woman behaved like O, but in her serum anti-B was lacking. By absorption-elution technique the very weak B activity was revealed. The saliva contained B and H substances, although the B to H ratio was significantly reduced, when compared to the normal B and Bm secretors. In the serum B transferase activity was not demonstrated. The presented results were comparable to those described in persons with Ay phenotype. Therefore, this weak B variant can be classified into By category.