There can be numerous challenges when assessing cell health in freshly harvested peripheral blood mononuclear cells (PBMCs, also called white blood cells or WBCs). The hemocytometer is the most commonly used instrument for determining cell concentrations. However, the task is tedious, requires careful cleaning and handling of the hemocytometer, and is subject to variation between users. Furthermore, blood is a rather complex sample type, as it contains various components that can lead to difficulty in manual cell counting. Use of an automated cell counter, such as one of the Invitrogen Countess II Automated Cell Counters, can significantly improve the accuracy of results while saving time over manual cell counting. The new Countess II Automated Cell Counter is a benchtop assay platform equipped with state-of-the-art optics, full autofocus, and image analysis software for rapid assessment of cells in suspension. Accurate - Use the Countess II Automated Cell Counter to eliminate the subjectivity of manual cell counting and user-to-user variability Fast - The Countess II Automated Cell Counter counts live and dead cells and measures viability and average cell size in as little as 10 seconds Convenient - The Countess II Automated Cell Counter requires no cleaning or routine maintenance. A capacitive touchscreen and simple user interface provides quick startup and requires minimal training.