Objective: Cancer and its treatment are highly stressful events that may significantly affect the daily emotional well-being of patients and their informal caregivers. Patient- and caregiver-reported received and provided support may contribute to both dyad members' fluctuation in daily affect, but few studies have examined these associations from a dyadic perspective so far. The current study examined predictions derived from 3 theories on patterns of relations between subjectively assessed dyadic provided and received support and daily affect within dyad members: (a) invisible support theory, (b) the suggestion that providing support may be better than receiving it, and (c) beneficial supportive equity. Method: Actor-partner interdependence models were tested using 28-day diary data from 200 patient-caregiver dyads. Diary assessments started on the first day following patients' discharge from the hospital, that is, about 3 weeks following patients' hematopoietic stem ceil transplantation (HSCT). Results: Daily invisible support was not related to more positive indicators of patients' or caregivers' daily affect. For patients' affect, findings generally supported the hypothesis of psychological benefits of support provision over receipt, in both concurrent and lagged analyses. For caregivers, visible received support from patients and supportive equity (i.e., both provided and received support relatively high), both concurrently and lagged, were related with better emotional state. Conclusions: The findings highlight the costs, benefits, and complexities of daily support transactions in dyads following HSCT, thus indicating the practical implications of the study: the importance of screening for support needs and abilities in both patients and caregivers.