α-galactosyl 1, 3 galactose was a better inhibitor of precipitation than galactinol which in turn was better than α-galactosyl-1,6-N-acetylglucosamine in both the B-anti-B and BP1-anti-BP1 systems. Since the B and BP1 determinants are distinct and since melibiose behaves quite differently as an inhibitor in these two systems, an unambiguous interpretation as to the second unit in these two determinants cannot as yet be made.