 1998 John Wiley & Sons, Inc. CCC 0012-1630/98/010093-09 Michelle de Haan Cognitive Development Unit Medical Research Council London, WC1H 0BT, UK M egan R. Gunnar Kathryn Tout Jordan Hart Institute of Child Development University of Minnesota Minneapolis, MN 55455 Kathy Stansbury Department of Psychology University of New Mexico Albuquerque, NM 87131 Familiar and Novel Contexts Yield Different Associations between Cortisol and Behavior among 2-Year-Old Children Received 11 July 1997; accepted 29 September 1997 ABSTRACT: We examined 10:30 a.m. salivary cortisol levels in twenty-four 2-year-old chil- dren at home, and then at several points during transition into preschool: Week 1, Weeks 6– 9, and the 1st week following a month-long holiday break. Cortisol levels did not increase when the children first started school as compared to either home or later school levels. Cortisol levels were correlated across similar, but not across dissimilar, psychosocial contexts. Home levels were correlated with more shy, anxious, internalizing behavior, while the response to starting school was correlated with more assertive, angry, and aggressive behavior. Behavior was assessed using parent temperament reports, teacher reports, and observational measures. We conclude that HPA activity as indexed by salivary cortisol measures is differentially as- sociated with behavior in familiar and novel contexts. Consistent with our prior work, shy/ anxious behavior is not significantly associated with elevations in cortisol when young children enter new social situations.  1998 John Wiley & Sons, Inc. Dev Psychobiol 33: 93—101, 1998 Keywords: temperament, children, cortisol In recent years there has been a heightened awareness of the impact early experiences can have on brain de- velopment (e.g., Nash, 1997). One particular area of focus has been physiological responses to challenging, stressful events. Neurochemicals released in response to such events not only activate short-term adaptive Correspondence to: M. R. Gunnar Contract grant sponsor: NICHD Contract grant number: HD16494 Contract grant sponsor: NIMH Contract grant number: MH00946 responses (e.g., increasing available energy substrates such as glucose and amino acids; Munck, Guyre, & Holbrook, 1984), but can also have longer-lasting effects both directly on the stress-sensitive systems themselves as well as on other brain systems (Fuxe et al., 1996; McEwen, 1996; Meaney, et al., 1993.) Developmentally, these effects may be one way in which early experiences contribute to individual dif- ferences in brain organization and behavior observable later in life (Meaney et al., 1993). Many researchers in this area have focused on the effects of adverse and atypical early experiences such