The effects of corticotropin-releasing factor (CRF) and growth hormone-releasing factor (GRF) on electroencephalographic (EEG) and behavioral signs of sleep and wakefulness following intracerebroventricular (ICV) administration was investigated in adult male rats. Visual scoring of EEG records as well as spectral analysis revealed that CRF (0.0015-0.015 nmol) produced decreases in slow wave sleep concomitant with significant decreases in spectral power in lower frequencies (1-6 Hz) and increases in high frequencies (32-64 Hz). In contrast, GRF (2.0 nmol) produced increased EEG and behavioral signs of slow wave sleep associated with significant increases in spectral power in the low frequencies (1-2 Hz) and decreases in high frequencies (32-64 Hz). ICV administration of GRF was also found to produce decreases in locomotion when administered during the active part of the rats' circadian cycle. These EEG and behavioral findings seen following CRF and GRF are consistent with the behaviors frequently correlated with the known circadian timing of the release of corticosteroids and growth hormone during the sleep-waking cycle in rat and human.