Experts in the field of immunohematology will present a new collection of cases, some of which took decades to resolve and others that remain unresolved. The final (or most recent) explanation or conclusion may not always be agreed upon, even amongst these experts. These unique cases include antibodies demonstrating unusual activity, negative results where positive ones are anticipated, unusual clinical conditions, and the inability to identify blood group specificity using only red cells serology. Participants will have time for open discussion of the cases.