Research on the benefits of social support groups has been inconclusive. One reason is that individual differences in intervention responses have rarely been examined. The authors determined the extent to which individual difference variables moderated the effects of an information-based educational group and an emotion-focused peer discussion group on the mental and physical functioning of women with breast cancer (n = 230). The authors administered the SF-36 (S.E. Ware, K.K. Snow, M. Kosinski, & B. Gandek, 1993), a multidimensional quality of life instrument, pre- and postintervention. Educational groups showed greater benefits on the physical functioning of women who started the study with more difficulties compared with less difficulties (e.g., lacked support or fewer personal resources). Peer discussion groups were helpful for women who lacked support from their partners or physicians but harmful for women who had high levels of support. Implications of these results for clinical interventions are discussed.