Examined relations between reactivity (peak response) and regulation (response dampening) in 6-month-olds' cortisol and behavioral responses to inoculation. Found that reactivity and regulation were unrelated for both cortisol and behavior, suggesting both measures are needed to characterize more accurately infant response to stress. Found considerable variation in timing of the peak cortisol response, suggesting that a single poststressor cortisol sample is not a sensitive measure of cortisol reactivity. (Author/KB)