The burden of caregivers of patients suffering from of Alzheimer type dementia (DAT) and vascular dementia (VD) was analysed at the critical time, the "breaking-point", when home care becomes insufficient and/or inadequate and the caregiver burden has probably reached its upper limit. Primary family caregivers of 39 DAT and 40 VD patients who were being considered for relocation into group-living units were studied. Total caregiving burden and different aspects of the burden: general strain, isolation, disappointment, and emotional involvement, were correlated with the patients' diagnoses, abilities, and symptoms. Closer kinship to the patient imposed a heavier burden. The caregiver's gender, social class, and previous institutionalization of the patient did not influence the caregiver burden. There was no significant correlation between the patients' ADL ability or cognition and the burden. A higher level of disappointment was found among the VD carers. Different symptomatology in patients of the two diagnostic groups was related to special aspects of the burden. Multiple regression analysis showed that the amount of caregiving time each week and impaired sense of own identity, misidentifications, clinical fluctuations, and nocturnal deterioration in the patients predicted the breaking-point.