177 rats were handled, shocked, or unmanipulated throughout the preweaning period or for 20 days immediately after weaning. At 3 mo., plasma corticosterone levels were determined immediately or 0, 5, 15, 30, or 60 min. following reaction-to-handling tests used to evaluate emotional reactivity. Emotional reactivity of handled preweaning Ss was significantly less than that of shocked or control Ss. There was no consistency in the behavioral data of Ss manipulated after weaning. Handling and shock effected a significant attenuation of the plasma corticosterone response of preweaning Ss to behavioral testing. The data provided no evidence of a consistent relationship between emotional reactivity and plasma corticosterone levels. (PsycINFO Database Record (c) 2006 APA, all rights reserved)