Nutritive deprivation, suckling deprivation, gastronintestinal fill, and milk availability contribute to the control of sucking (as measured by jaw-muscle electromyograph) and ingestion of milk (provided via a tongue cannula) in 11-13-day-old rat pups. Depriving pups of the opportunity to suckle reliably increases subsequent sucking and milk intake. lntraoral delivery of milk also increases sucking, regardless of whether or not pups are suckling-deprived. Gastrointestinal preloads have no effect on sucking if pups are not receiving milk, but reliably block the increase in sucking which accompanies milk delivery. Finally, milk delivered to the pup's mouth prior to a suckling opportunity can either enhance or attenuate subsequent sucking depending on whether pups are allowed to consume milk whilc suckling. In all cases, a particular mode of sucking ("rhythmic" sucking) is most affected by experimental manipulation, and appears to be an important component of the pup's ingestive behavior.There are at least 2 ways that a suckling infant might control the amount of milk it consumes from the nipple. It might vary the amount of time it spends attached to the nipple or it might vary the frequency and intensity of its suckling while on a nipple. Infant rats do not appear to employ the 1st strategy until they are about 15 days old. Before this age, a pup's latency to attach to a nipple, the time it spends attached to a nipple, and the number of times it will shift from 1