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Analysis of autonomic nervous system activity is a subject of increasing interest in the fields of health care and handicap management, as it provides information on the emotional, sensorial, and cognitive states of the patient. In this context, the simultaneous measurement of several physiological signals using small, discreet, mobile devices is required, in order to unobtrusively obtain such information under real-life conditions. We have therefore developed an ambulatory device which enables the measurement of heart rate, electrodermal activity, and skin temperature with noninvasive sensors. Wireless communication and local data storage on a memory card enables the device to be used during in-situ experiments for the analysis of autonomic nervous system activity. We have used this instrumentation in a study for the objective evaluation of stress in the blind when walking in urban space, through the analysis of electrodermal activity of blind pedestrians who independently followed a charted course involving a range of urban conditions. Experimenting in real-life settings has lead to the definition of novel, more pertinent parameters for the analysis of physiological signals in the study of autonomic nervous system activity. Results from these experiments have identified, for the first time, some rather surprising obstacles or events which give rise to an increased stress for the blind. These results were very encouraging for the use of such ambulatory devices for experiments under real- life conditions.