HIV/AIDS is one of the most destructive pandemics in human history, responsible for more than 25 million deaths. More than 30 million people live with limited or no access to therapeutic treatments, mainly due to the high cost of highly active antiretroviral therapies (HAART) and current diagnostic tests as well as due to the lack of basic infrastructure (e.g. lack of electricity, no trained personnel) that can support these tests. The need for innovative, inexpensive diagnostic instrumentation technology that can be used in resource-limited settings is immediate.While programs that offer free HAART are being implemented in resource-limited settings, no diagnostic tests are available for evaluating the efficacy of HAART provided for the reasons mentioned above. Efficient management of HAART requires monitoring the course of HIV infection over time. The World Health Organization (WHO) recommends the CD4 T-cell count test for monitoring the clinical status of HIV individuals in resource-limited settings.We propose to develop a portable, inexpensive, MEMS (MicroElectroMechanical Systems)-based, imaging system for counting the absolute number of CD4 cells from 1 l of whole blood. We use the term ‘imaging system’ to denote the different approach we follow for counting CD4 cells: rather the reading one by one singles cells (as it is done with flow cytometry), our system can image simultaneously thousands of individual cells, pre-assembled on the surface of a biochip. Although the proposed imaging system can replace current expensive cell counting instrumentation, our goal is to develop a system that can reach the end-user wherever limited infrastructure is present and no access to a hospital or clinic is possible. Such technology will not only enable to monitor the efficacy of an individual’s HAART in the developing world, but it will make more medicines available by identifying patients who need a treatment from patients who do not need it.