Rats deprived temporarily of maternal contact and nutrition from the 3rd to 14th day of life showed decreased emotionality and poor memory capacity when tested in adulthood. Simultaneous administration of choline chloride, an acetylcholine precursor, in neonatal life permanently increased the emotionality and restored memory capacity to levels of control animals. However, no effect was demonstrated when choline chloride administration occurred after the deprivation period. The results of this study reveal that the effects on later behaviour appear to be dependent on the timing of choline chloride exposure in early life. Profound and long-lasting abnormalities in brain function produced by early postnatal maternal deprivation can be attenuated by correcting abnormal acetylcholine levels during brain development. Hence, acetylcholine can be considered as an important, environment-dependent local organizer of the brain.