It was hypothesized that combined individual child vulnerability (anxious solitude) and interpersonal stress (peer exclusion) would predict the strongest responses to experimentally manipulated behavioral peer rejection. Results indicated that in a sample of 3rd graders (N = 160, 59% girls), anxious solitary excluded children displayed more behavioral manifestations of social helplessness before and after behavioral rejection, reported more feelings of rejection in anticipation of and reaction to behavioral rejection, and were observably more upset during behavioral rejection than were normative children. Moreover, affective responses to behavioral rejection mediated the relation between anxious solitary excluded status and behavioral manifestations of social helplessness. Furthermore, anxious solitary excluded children versus anxious solitary children demonstrated excessive suppression of vagal tone and more sustained acceleration in heart rate during the experiment. Results also indicated that affective, social-cognitive, and regulatory processes directly contributed to children's responses to behavioral rejection. (Contains 1 footnote, 7 tables, and 6 figures.)