Psychopathic and neurotic delinquents were subjected to perceptual isolation (PI) and arousal (A) and were given pre- and postmeasures of novelty, complexity preference, and anxiety. The results showed that (a) there was a significant negative correlation between novelty preference and anxiety level and between complexity preference and anxiety level; (b) the psychopathic delinquents had significantly lower pretest anxiety and significantly higher novelty and complexity preference scores; (c) after PI psychopathic delinquents increased their complexity preference scores significantly more; and (rf) after A psychopathic delinquents did not shift scores, while neurotics significantly increased anxiety scores and decreased complexity preference scores. This investigation was concerned with the preference behavior of psychopathic and neurotic delinquents for novelty and complexity of stimuli under experimental conditions of perceptual isolation and arousal. Its principal aim was to test the validity of a theory concerning the etiology of psychopathy proposed by Quay (1965) which holds that the psychopathic personality represents pathological stimulus seeking. Quay (196S) states: We are suggesting that the level and variability of sensory inputs which are necessary for the maintenance of pleasant affect are much greater for the psychopath than for the ordinary individual [p. 181]. In order to