A pure deficiency of thiamine was produced in rats, and their neurological and cardiovascular symptoms, and body temperature were observed by means of electromyograph, electrocardiograph, and thermocouple respectively. These results were contracted with histological finding and changes in various blood components. Similar experiments were carried out with the control group of underfed rats for the purpose of checking the influence of inanition, which always came into question in the experimental thiamine deficiency. Basic general observations were first made on normal, thiamine-deficient, and control underfed rats. In the thiamine-deficient group anorexia and body weight decrease developed from the end of the second week, paralytic and gastrointestinal symptoms (diarrhea) appeared from the fourth week, and the animals died in the fifth week. Oral administration of thiamine in a daily dose of 5 μg in the end stage of thiamine deficiency caused increase in appetite and body weight on the next day, and cured the paralytic and gastrointestinal symptoms in several days. The effect of single injection of thiamine one mg lasted for two weeks. In the control underfed group the change in body weight was similar to that of thiamine-deficient group, but appetite and vitality were good till end. Paralytic and gastrointestinal symptoms were not observed, and almost all animals died in the sixth week.