Hypoglycaemia is the most common complication affecting people with Type 1 insulin dependent diabetes mellitus. Its onset is characterized by symptoms which include sweating, tremor, palpitations, loss of concentration and tiredness. As part of a research project to investigate the mechanisms of hypoglycaemia we have developed an ambulatory system to monitor and. record pulsatile changes in blood flow, pulse internal, body temperature and skin impedance. The system uses a pocket computer (Atari Portfolio) to collect and store the data on a memory card. The analogue system consists of two thermocouples, an infrared photoplethysmograph and skin impedance monitoring circuit. To conserve power the system is programmed to make measurements for 2 min every 10 min; using this regimen over 16 h of data can be stored. Data collected during a spontaneous overnight hypoglycaemic episode are presented and also a comparison between continuous and intermittent data collection during a period of induced hypoglycaemia. The system is being used to investigate the physiological responses to hypoglycaemia but could easily be adapted for monitoring other physiological signals.