Researchers have expressed considerable interest in the question of whether positive or negative social exchanges more strongly affect psychological health, but previous studies have been limited by using nonparallel measures of positive and negative social exchanges, by measuring negative affect only, and by relying largely on cross-sectional designs. The independent effects of positive and negative exchanges on both positive and negative affect were examined in a short-term longitudinal study of 277 older adults, using social exchange measures with parallel content and equivalent reliability and validity. In cross-sectional analyses, positive exchanges predicted positive affect, and negative exchanges predicted negative affect. In longitudinal analyses, however, negative exchanges predicted both positive and negative affect, whereas positive exchanges were unrelated to either outcome. The more potent and longer-lasting effects of negative exchanges have important implications for theory and interventions.