This article summarizes studies relating the trait of sensation seeking to electrodermal and heart-rate responses and cortical evoked potential arousal. Stimulus factors of novelty, intensity, and stimulus significance are important. High sensation seekers tend to give stronger physiological orienting responses than lows to novel stimuli of moderate intensity, particularly when such stimuli are of specific interest. Lows tend to show defensive responses as defined by heart-rate acceleration. The cortical reaction of the highs tends to be augmented by intense visual or auditory stimuli, while that of the lows tends to be reduced or unresponsive to variations in stimulus intensity. Differences between psychophysiological responses of high and low sensation seekers are interpreted as reflective of different evolved biological strategies for processing novel or intense stimulation.