Proficiency testing is a concept with which all testing laboratories are familiar. However, when testing is being performed on cellular therapy products, proficiency programs become much more complicated. Measuring properties of live cells presents challenges that do not exist for chemical analytes. Furthermore, the relatively small number of laboratories performing testing of cellular therapy products and the wide array of test methods can make interpreting inter-laboratory comparisons difficult. This audioconference will take a detailed look at the challenges of proficiency testing for cellular therapy laboratories.