The authors evaluated the changes in the scores on Hasegawa's rating scale for dementia (HRSD) of demented patients in a hospital for dementia. The subjects in this study were 69 patients (12 males and 57 females) including 34 with dementia of the Alzheimer type (DAT), 30 with multi-infarct dementia (MID) and 5 with mixed dementia. Their average age was 75.6 years and the mean period after symptom onset was 2.5 years. The observation period was 5 months after admission to the hospital. We rated HRSD on admission and each month after admission. During the observation period, 65 patients received drugs orally and 65 patients were given rehabilitation for impaired cerebral function. We tried to classify the pattern of change in the HRSD into 5 groups as follows; 1) no remarkable change or deterioration, 2) wavering, 3) improvement during only the first month, 4) improvement from the first month after admission, 5) improvement from admission. We assumed that the patients in group 3) had been underestimated on admission. Their mental states might have been confused on admission because of the change in their living environment. Thus we rejected this group for statistical analysis and compared the medical characteristics of those in the non-improved group (1 and 2) with those in the improved group (4 and 5). The period from onset of symptoms in the improved group was shorter than in the non-improved group (p less than 0.05). Moreover there was a tendency (p less than 0.1) toward less abnormal findings in the EEG and less cerebral atrophy on CT scan in the improved group.(ABSTRACT TRUNCATED AT 250 WORDS)