The development of technology for use in resource-poor countries encounters a specific type of challenge not ordinarily faced in academic science: the technology must be inexpensive and it must work with minimal infrastructure. This challenge is particularly severe when the problems being solved are, by their nature, ones that require high-technology solutions. For these kinds of problems, the elegance of the solutions must lie in the use of science to guide the assembly of readily available components into a simple, workable, and well-integrated package. In this paper, we describe an integrated approach to a miniaturized immunoassay called a “POCKET immunoassay” (“POCKET” is short for portable and cost-effective). This immunoassay has, we believe, the potential to be inexpensive and operable with minimal equipment and technical skills, and shows an analytical performance approaching that of enzyme-linked immunosorbent assays (ELISA) performed in a bench-top format in clinical laboratories. A top priority for improving health in developing countries is technology for simple, affordable diagnosis of infectious diseases. Immunoassays such as ELISA are the most reliable and widely used methods for detecting antigens and antibodies, but they require expensive and bulky instruments for optical detection, hours of incubation for diffusionlimited reactions on the surface, and many steps of pipetting. 3] These constraints prevent the use of ELISA in settings that require low-cost or compact equipment, and in environments that lack electricity or trained personnel. One application with these requirements is the detection of infectious diseases in the field in developing countries; 4,5] other potential uses include point-of-care diagnostics by first responders and in health clinics, and detection of biological warfare agents in the field. Immunochromatographic assays (also known as “strip tests” and “lateral-flow