Individual differences in adult attachment have been the focus of recent research on personal relationships. Research has indicated that those with insecure attachment histories were more threatened by a partner's attraction to a rival than were persons reporting secure parental attachment. Higher levels of dispositional jealousy have also been found to be correlated with depression. It was predicted that person and situation variables would be associated with differences in cognitive and affective responses to imagined scenarios involving a rival to a romantic relationship. Subjects (N=134) were undergraduate students who were currently involved in romantic relationships. Subjects imagined a control scene of their partner and their relationship and one of three scenes presenting varying levels of threat to the relationship by a third person. A main effect for attachment was found. Subjects, regardless of level of threat to their relationships, who described themselves as secure in attachment relationships, reported greater joy and perceived relationship security, power, and perceived attractiveness to their partners, and lower levels of jealousy and other negative affects. Situation also yielded a main effect. Jealousy, negative relationship perceptions and emotions were evoked when the threat to the relationship by a rival was highest. Additional findings regarding depression, appraisal of threat, and coping suggest differences in mental health adjustment between attachment types. (Author/LLL)