Parental supportiveness and protective overcontrol and preschoolers' parasympathetic regulation were examined as predictors of temperamental inhibition, social wariness, and internalizing problems. Lower baseline vagal tone and weaker vagal suppression were expected to mark poorer dispositional self-regulatory capacity, leaving children more susceptible to the influence of parental socialization. Less supportive mothers had preschoolers with more internalizing problems. One interaction between baseline vagal tone and maternal protective overcontrol, predicting social wariness, conformed to the moderation hypothesis. Conversely, vagal suppression moderated several links between paternal socialization and children's anxious difficulties in the expected pattern. There were more links between mothers' self-reported parenting and child outcomes than were noted for direct observations of maternal behavior, whereas the opposite tended to be true for fathers.