A computer-based system for collecting, processing, and analyzing pressure transient data has been developed. Primary components include downhole pressure sensors, linedrivers, a micro-computer, data storage disk, scanner, frequency counter, digital voltmeter, power supply, graphics plotter, and printer. In-field data processing and analysis greatly aid in handling the large volume of data that are collected during pressure transients tests, particularly the multiwell interference tests that are so important for characterizing and assessing geothermal reservoirs. In-field data processing provides the field engineer, on a real-time basis, with the information needed to make decisions regarding test parameters and duration. The system has been used on numerous occasions and has proved itself to be reliable under the harsh operating conditions that are usually encountered in the field. This paper describes the advantages of using this type of system for collecting data, the components and configuration of the system, and the software programs used to collect and process the data. Finally, two field applications are presented.