I. Introduction Measures of skin potential level and changes in response to stimulus conditions have been used in psychological research much less often than have measures of skin resistance or skin impedance. To a large extent, this has been due to lack of adequate instrumentation. However, in recent years greatly improved instrumentation has become available making feasible accurate recording of skin potentials. From a theoretical viewpoint, the potential measure appears the measure of choice, since it imposes no external current on the physiological system under study, whereas resistance and impedance measures are known to be a partial function of the frequency and magnitude of the imposed current.2 In both research and clinical use of electrodermal measures of skin activity, the level of ongoing activity as well as transient responses in level are of interest. The significance of initial level for the evaluation of any