Habituation of an orienting response in rat pups was used to study the development of the anterior commissure (AC) and its role in olfactory memory. Six- and 12-day-old pups received odor presentations to one side of their olfactory system and were tested later for habituation to additional presentations made to either the trained or untrained side. Six-day-old pups remembered only on the trained side. Twelve-day-old pups remembered when tested on either side. Transection of the AC in 12-day-old pups before, but not after, training prevented the transfer of memory. Thus, between 6 and 12 days of age, olfactory cross-projections carried in the AC mature and provide a functional substrate for transfer, at the time of training, of a form of olfactory learning.