Sleep/wake states were investigated in rat pups at 12-13 days of age following deprivation of milk and their dam for 9-12 hr. Early in the deprivation period each pup was equipped with bipolar stainless steel electrodes for electroencephalographic (EEG) and electromyographic (EMG) recordings. Four groups of pups were tested using anesthetized dams. The pups were either allowed to root in the dam's fur, but were not allowed to attach to a nipple; allowed to root after receiving a gut load of rat's milk; allowed to attach and suck a nipple without receiving milk; or allowed to attach and suck a nipple following a gut load of rat's milk. The results indicate that suckling elicits sleep, especially slow-wave sleep. Milk in the gut enhanced paradoxical sleep, primarily in the context of sucking. This experiment confirms that the types of sleep can be affected separately by specific internal and external events. The shift in the sleep/wake condition to slow-wave sleep in the suckling situation suggests one type of satiety. Furthermore, the selective enhancement of paradoxical sleep following the gut load of milk suggests postingestive satiety.