This study examined whether early isolation (EI), early handling (EH), or early nonhandling (NH) in infant rats alters (a) prepulse inhibition (PPI) of the acoustic startle response (ASR) or its disruption by apomorphine, (b) motor activity or its stimulation by amphetamine, or (c) corticosterone activity (because of its modulation of dopamine activity), in adulthood and in comparison with a normal-husbandry postnatal control environment. EI did not affect PPI, reduced PPI disruption by apomorphine in males, and increased amphetamine-stimulated activity in males. NH increased the ASR, reduced activity in the open field, and increased corticosterone reactivity in males. In all paradigms, the effects of EH were similar to those of the control environment. This study provides an important contribution to the evidence on the relationship between postnatal experience and long-term neurobehavioral development in the rat and the relevance of this approach to animal models of neuropsychiatric disorder.