Forty-three subjects with mild senile dementia of the Alzheimer type (SDAT, so-called probable Alzheimer's disease) were studied longitudinally by serial administration of several tests to rate dementia. Comparison was made with 58 healthy elderly controls. The clinical diagnosis was confirmed in all 16 autopsies. At 5 years after entry into the study, the cumulative rate of nursing home placement was 73%, and of death, 30%, rising at 7 years to 84% and 44%, respectively. Four of six clinical measures of dementia were found to correlate with the natural history of SDAT. Several measures are better than a single one in carrying out longitudinal studies of the disorder.