A complete potentiometric alternating biosensor system (PAB) is described which utilizes a newly developed transducer based on the light addressable chemical sensor (LAPS) technology, following detailed theoretical optimizations of the relevant physical parameters. Our device, entirely designed and realized 'in house', combines measuring chambers with specific electronic cards and the related software programs; the system is completely automated and driven by a personal computer. The electronics was designed in order to obtain a good general signal-to-noise ratio, hence ensuring reproducible results. The software package consists of low-level programs (written both in C and in Assembler) to interact with the data acquisition and controlling cards, and of high-level programs (written in C) to get, display, save and print data files, and to present a suitable user interface. A very important peculiarity of our system is the possibility of connecting different measuring chambers to the same device. This allows the user to perform a wide variety of experiments, utilizing different biological elements, by simply changing the reaction chamber and selecting the appropriate acquisition software. The system has been shown to operate with living cells as well as with enzymes and antibodies. In addition, a particular chamber containing a gold-evaporated transducer can be connected to the main system, allowing redox potential measurements. The system utilizes a fast information recovery from the transducer output signal, and can acquire quantitative data every few fractions of a second. This feature can be utilized to monitor fast acidification or redox processes.