Examined whether early differences in stress reactivity were related to self-recognition at 18 months. Found that self-recognition was related to greater cortisol response and less rapid quieting at 6 to 18 months, whereas cortisol and quieting responses of 2- to 4-month-olds did not differentiate self-recognizers and non-self-recognizers, suggesting a role for temperament differences in facilitating self-recognition emergence. (Author/KB)