Examined the relations among adrenocortical stress reactivity, infant emotional or proneness-to-distress temperament, and quality of attachment in 66 infants tested at 9 and at 13 months. Performed the Louisville Temperament Assessment at 9 months and conducted the Strange Situation at 13 months. Adrenocortical activity was not associated with attachment classifications. Emotional temperament at 9 months was strongly correlated with emotional temperament at 13 months. There was also evidence that at both ages infants who were more prone to distress experienced greater increases in adrenocortical activity during the laboratory tests. Significantly, however, although both the Louisville Temperament Assessment and the Strange Situation involve maternal separation (a potent stimulant of the adrenocortical system in nonhuman primate infants), we noted only small elevations in cortisol, and these elevations were significant only at 9 months.