All too often, serologists encounter reactivity with no apparent specificity during pre-transfusion testing. What additional testing should be performed? How extensive must the testing be? How do you ensure that adequate testing is performed in order to assess for a weakly reacting alloantibody of clinical significance? What do you do when the extraneous reactivity cannot be explained? The speakers, both experts in the field of red cell serology, will describe problem solving techniques and logical approaches to these serological questions and dilemmas. Case studies will be used to compliment the lecture material.