More than 35 million HIV-infected people live in the developing world, where resources are scarce. The World Health Organization has stated that there is an urgent need for a handheld, reliable, low-cost counting device to monitor CD-4 T lymphocytes in patients and deliver immediate results in the field. This project is developing a low-cost, disposable, point-of-care device utilizing a microchip to analyze a finger-stick blood-drop sample to produce a CD-4 count in less than a minute. Accelerating CD-4 counting in resource-limited settings has the potential to dramatically improve standards of HIV care while reducing costs of treatment. Such a technology would have significant applications in the developed world as well.