Molecular Devices Corporation (MDC) proposes to explore the feasibility of a novel design for an inexpensive detector configured for rapid measurement of optical density in microtiter plate and microtiter format filters. This proposed device, based upon a monolithic photodetector and light emitting diodes, is envisioned for use in research, clinical, and industrial laboratories requiring multiple, simultaneous repetitive assays. Compared with currently available instruments this device will be significantly lower in price, more rapid and convenient, and provide a means to quantitate the optical density of colored reagents directly on filter papers. In Phase I research MDC intends to: (1) explore various configurations of the photodetector to optimize signal to noise ratio; (2) determine photometric linearity; and (3) define optical sensitivity. Two sets of experiments relating to microtiter plates and microtiter filters will be conducted. Emphasis will be placed upon the development of a system to quantitate accurately blood reagents on filter paper. An extension of this research would be the development of the capacity to perform multiple kinetic analysis which cannot be done on commercial instrumentation and which has wide application in biomedical research and laboratory medicine.