The spouse caregivers of 406 patients with Alzheimer's disease were randomly assigned to an enhanced counseling and support intervention or to a usual care control condition. Structured interviews were conducted to assess changes in social support and psychosocial outcomes for the 312 caregivers who provided care in the home for at least 1 year. The number of support persons, satisfaction with the support network, and support persons' assistance with caregiving all increased significantly as a function of the intervention. Structural equation models indicated increased satisfaction with the social support network mediated a significant proportion of the intervention's impact on caregiver depression. A portion of this mediated effect was further mediated by changes in caregiver stress appraisals. Implications for strengthening intervention programs for spouse caregivers of individuals with Alzheimer's disease are discussed. Copyright 2005 by the American Psychological Association.