Aim: The purpose of this study was to demonstrate the effectiveness of intermittent fluid infusion (intermittent rehydration therapy) to dehydrated elderly patients and the efficacy of Heisei Solution Water (HSW), an oral and enteral rehydration solution developed by our group. Methods: We enrolled 375 elderly patients with suspected dehydration from among 1,921 patients of our hospital and 13 affiliated hospitals. A total of 36 of 375 patients received intermittent rehydration therapy. These patients were then divided into 3 groups according to the method of administration: (1) oral and enteral administration (n=16), (2) intravenous administration only (n=10) and (3) combined oral, enteral and intravenous administration (n=10). We then compared blood urea nitrogen/creatinine (BUN/Cr) ratios among the 3 groups. Results: BUN/Cr ratios were improved in all groups, but there was no statistically significant difference in the degree of improvement of BUN/Cr ratios among the 3 groups. Conclusion: Intermittent rehydration therapy is a highly effective way to manage dehydration. The intermittent oral and enteral administration of HSW demonstrated the same effectiveness as other forms of administration. FULL-TEXT AVAILABLE IN PUBMED.