Three antisera are reported that reacted with all cells tested except the donor’s own and those from K(0) people. Each serum reacted with the cells of the other two donors. The nature of the association of the three antibodies with the Kell system remains unknown.

A new antibody, named anti-K12, reacts with a high-frequency red-cell antigen associated with the Kell blood groups. Two examples have been found, both in people having the phenotype K-k+, Kp(a-b+), Js(a-b+). Anti-K12 reacted with all of 1,000 random blood samples, less strongly with some Kp(a + b-) samples, weakly with red cells of the McLeod phenotype and not at all with K0 red cells. It reacted weakly against red cells from children with chronic granulomatous disease with weak Kell antigens. While the data establish a phenotypic association between the K12 antigen and the Kell system, there is no evidence to show whether K12 is an inherited character, and, if so, whether the controlling gene is part of the Kell complex.