To avoid the stress encountered during oral drug administration, we implanted chronically a catheter into the stomach, and recorded electroencephalogram (EEG) and electromyogram, in freely moving rats to evaluate their sleep-wake pattern. Rats with catheters in their stomach did not exhibit any changes in sleep-wake profiles in terms of sleep amount, number of episodes and EEG power spectra. When administered through the catheter, caffeine (6mg/kg) statistically increased wakefulness, as compared with the vehicle control. However, when given orally by hand restraint and gavage, it caused no increase in wakefulness, owing to the masking effect of this method, which caused increased wakefulness when saline was used by handling animals. These results indicate that oral administration through a chronic stomach catheter is a useful way for evaluating wake-promoting components.