Louis A. Schmidt Nathan A. Fox Behavioral and Kenneth H. Rubin Institute for Child Study University of Maryland Neuroendocrine College Park, MD 20742 Esther M. Sternberg Responses in Philip W. Gold Craig C. Smith Shy Children Neuroendocrine Immunology & Behavior Unit Clinical Neuroendocrinology Branch National Institute of Mental Health Bethesda, MD 20892 Jay Schulkin Behavioral Neuroscience Unit Clinical Neuroendocrinology Branch National Institute of Mental Health Bethesda, MD 20892 Received 20 July 1995; accepted 13 March 1996 ABSTRACT: Previous research has shown that infants who display a high frequency of motor activity and negative affect at 4 months of age are likely to be behaviorally inhibited toddlers. We examined social behaviors, maternal report of temperament, salivary cortisol, and baseline startle responses at age 4 in a sample of children, some of whom displayed a high frequency of motor activity and negative affect at 4 months of age. Infants who displayed this temperamental profile were reported by their mothers as more shy at age 4 compared with other children. We also found that 4-year-olds who displayed a high frequency of wary behavior during peer play exhibited relatively high morning salivary cortisol, were reported as contemporaneously shy by their mothers, and were behaviorally inhibited at 14 months of age. There were no significant relations found between baseline startle and morning salivary cortisol and measures of shyness at age 4. We speculate that high levels of cortisol in shy children may induce changes in the amygdala, exacerbating their fearfulness.  1997 John Wiley & Sons, Inc. Dev Psychobiol 30: 127–140, 1997 Keywords: temperament; fear; behavioral inhibition; shyness; startle; salivary cortisol; amygdala INTRODUCTION Correspondence to: L. A. Schmidt or N. A. Fox Contract grant sponsor: John D. and Catherine T. Behavioral inhibition reflects a tendency to dis- MacArthur Foundation play fear and wariness in response to novel stimuli. Contract grant sponsor: National Institutes of Health Contract grant number: HD 17899 Behaviorally inhibited children display long laten-  1997 by John Wiley & Sons, Inc. CCC 0012-1630/97/020127-14