Ambulatory treatment for cancer has increased patients' self-care requirements and placed demands on family members to manage the illness and treatment side effects at home. This exploratory study was undertaken to assess family caregiving demands (load) and to examine caregivers' appraisals of the illness/ caregiving experience. Forty-seven persons involved in the care of patients receiving radiotherapy for cancer were observed. Appraisal of stress was measured with the Appraisal of Caregiving Scale (ACS). This newly developed measure, derived from cognitive appraisal theory, is designed to assess the intensity of four possible appraisals of caregiving: harm/loss, threat, challenge, or benign. Participants also completed the Caregiver Load Scale, a measure of the time spent in caregiving activities. Satisfactory reliabilities were obtained for both measures. Family caregivers reported spending the most time in providing transportation giving emotional support, and in extra household tasks. They received the most assistance from family and friends, and made minimal use of professional services. Caregiver load was correlated positively with the length of time on treatment and with patient dependency. Caregivers in the poorest health, those with less education, and those of lower socioeconomic status had higher scores on the ACS appraisals of harm/loss and threat. Older caregivers had significantly higher challenge and benign appraisals. There was a strong positive correlation between caregiver load and the harm/loss and threat appraisals. Findings suggest a need for frequent reassessment of demands on family caregivers throughout the course of treatment and offer direction for future research.