Dietary free-glutamate (Glu) improves taste and palatability. In our previous study, we found that Glu intake by hospitalized elderly was low and supplementation of monosodium L-glutamate (MSG) to their staple diet improved their behavior. To confirm such findings, we conducted a double-blind and placebo-controlled trial in hospitalized elderly. The study consisted of a 1-month lead-in period, a 3-month intervention period, and a 1-month follow-up period. In the intervention group, 0.5% (w/w) MSG was added to every staple diet, 150 g of rice gruel (the MSG group). Fourteen subjects in the MSG group (average age 83.0 +/- 8.9 years) and 15 in the control group (average age 84.3 +/- 9.6 years) completed the study. The subjects of both groups took most of the given foods based on the energy requirement of each subject's metabolic rate, body weight, and activity. In the last week of each period, nurses assessed the dementia score and daily performance of both groups. The daily performance was improved by dietary MSG. Behavior during mealtime was video-recorded for 5 min in the lead-in period and after 3 months in the intervention period. Significant improvement in the mealtime behavior was observed only in the MSG group. Furthermore, although serum albumin itself did not increase, the ratio of reduced-form albumin to total albumin increased only in the MSG group. In conclusion, supplementation of 0.5% MSG to rice gruel three times a day for 3 months improved behaviors and the nutritional status of hospitalized elderly.