Proposed measures of autonomic nervous system functioning within an individual were reviewed. An important factor in the choice of such measures is the recognition that the magnitude response to stimulation is influenced, to a large extent, by the state of the individual prior to stimulation. From the point of view of informational content, there is little difference between the use of the magnitude change score and response level as the basic response datum when used in conjunction with the initial level. Consideration of the concept of the autonomic lability score as well as the mean response score reveals that neither measure adequately corrects nor compensates for the effect of prestimu-lus level. Several magnitude measures suggested for the comparison of individuals include the slope of the regression of change score on initial level, variability around this line, a measure of discriminability, and a measure of maximal reactivity. The temporal aspects of the autonomic response are discussed and, because of their lack of dependence on prestimulus level,two measures are extracted for each aspect[long dash]the mean and variability.