Behavioral and physiologic indices of arousal to auditory stimuli were examined during the first cycle of sleep in 8–12-year-old hyperactive children and nonhyperactive controls. No behavioral responses or sustained awakenings were obtained for any child during the first cycle of sleep to stimuli at intensities up to 123 dB sound pressure levelre0.0002 dynes/cm2),i.e., at intensities more than 90 dB above waking threshold values. Half of the arousal attempts in stage 2 and a quarter of those in stage 4 elicited a partial or momentary physiologic arousal response (i.e., EEG desynchronization and/or change in skin potential response or respiratory activity rates). These arousals were shortlived, with the subjects returning to sleep even with continuing or increased stimulus intensity. Neither the incidence of partial arousals nor the associated threshold intensities differentiated subject groups. Although increased skin potential response activity and decreased respiratory rates were observed during sleep relative to wakefulness, and a predominance of skin potential response activity was noted in stage 4 sleep, no significant differences in frequency (rate/min) of autonomic response measures were obtained when rates before and during auditory stimulation were compared.