Abstract
A cold agglutinin, Fl, reacted with an erythrocyte antigen, which was inactivated by neuraminidase. It resembled anti-I antibodies in reacting more strongly with erythrocytes of adults than with cord blood cells. However, unlike I, this ‘new’ antigen is destroyed by neuraminidase treatment. This antigen is also distinct from Pr, Gd and Sa type antigens which are equally expressed on cord and adult erythrocytes.