To older blood bankers, paternity testing (“relationship testing”) is a quaint thing that some of us “used to do.” Serologic red cell antigen testing has been replaced by sophisticated DNA testing methods. Historically, we would evaluate a purported father’s antigens and compare them to the antigens on the mother and baby’s red cells, and look for either a direct or indirect exclusion of that man as the father of the child (click the links for the specific definitions). Today, we really only see this on examination questions!