OBJECTIVE: Persons who provide care for individuals with chronic mental illness experience both objective burden (observable, tangible cost) and subjective (perceived) burden. This study sought to determine the relative power of behaviors of chronic mentally ill clients, behaviors required of caregivers, and demographic characteristics of both groups in predicting burden. METHODS: A total of 189 caregiver-client dyads were studied using a cross-sectional, correlational design. Caregivers were interviewed by phone about clients' needs for help in nine areas and about seven potentially troublesome client behaviors. Correlation and regression analyses were used to determine relationships among variables. RESULTS: Caregivers reported much less subjective than objective burden, although the relationship between the two types of burden was not consistent across the various areas in which clients needed help. Overall, more of the reported burden was related to caregivers' behaviors (their day-to-day tasks) than to clients' behaviors. Burden was greatly increased for caregivers who lived with the client. Caregivers most at risk for burden were those who lived with male clients who threatened suicide. CONCLUSIONS: Caregivers become accustomed to the stabilized behavioral profile of the client. Mental health professionals should be sensitive to profiles and situations that may produce increased objective and subjective caregiver burden.