The outcomes of children's exposures to others' positive and negative emotions were examined developmentally. Twenty-four infants in three age cohorts (10, 15, and 20 months old) were studied for 9 months. Mothers reported the child's reactions to naturally occurring events in which emotions were expressed; in addition, each week mothers simulated one specified affect (e.g., crying, anger, laughter), and an investigator portrayed affect incidents. Mother-child interactions were rated. The youngest children showed evidence of discrimination between others' positive and negative emotions. Responses to affect were examined as a function of the person expressing affect and the kind of affect. Sympathetic behaviors were directed toward the distressed mother but not the distressed investigator. In the natural setting, crying most frequently evoked sympathetic behavior; angry interactions turned the child away. In the oldest cohort there was individual consistency in sympathy over time. Mothers showing more positive contact in nondistress situations had children who were more sympathetic in distress situations. Socially out-going children were also more likely to comfort others in distress. Reparation behaviors (reactions to distress created by the child) appeared and increased with age. Theories of early altruism are discussed. (Author/JMB)