The psychophysiological literature on psychopathy is reviewed in the context of low-arousal theory. Difficulties in the theory are discussed both in general terms and specifically in relation to psychopathy. Contrary to the low-arousal theory, the data indicate that psychopaths exhibit a wider degree of variability in arousal levels and reactivity than normal indiciduals. A more accurate model of the disorder might be one in which psychopaths display a faster rate and a greater magnitude of change in physiological and behavioral activity than normals. It is suggested that psychopathy might be usefully viewed as a biochemical disturbance manifested in abnormal oscillations in neurotransmitter functioning, autonomic activity, and behavior. The literature is reexamined in light of this hypothesis, and a number of avenues for further research are discussed.