Monitoring physiological activity in freely moving subjects poses a considerable challenge. The Free-Range Physiological Monitor (FRPM) is a novel instrumentation pack designed to record and analyze physiological processes in ambulatory subjects for periods of 4 weeks and greater with no researcher intervention. Up to 255 monitors can be used simultaneously, with data compression ratios of up to 100:1 being achieved by data analysis being performed on the unit before the summarized results are transmitted by a 2 km range, 2.4 GHz radio link back to a base computer. Power for indefinite operation is provided by a solar panel. Currently the FRPM is being used to record the Auditory Evoked Response, electrocardiogram and body temperature to investigate stress levels in farm animals during transportation and handling for animal welfare studies.