In recent years, many cases of beriberi have been reported throughout Japan. One may assume that a great many healthy subjects suffer from a subclinical thiamine deficiency. The present study was carried out in order to examine thiamine status in 21 beriberi patients and 674 apparently normal subjects. In the beriberi patients the total vitamin B1 in whole blood and transketolase activity in the hemolysate were significantly lower, and the thiamine pyrophosphate effect was significantly higher, compared to normal subjects. However, these two groups could not be clearly separated by these biochemical parameters because of significant overlap. On analyzing the results of these biochemical parameters by discriminant analysis, beriberi could be diagnosed with an accuracy of 87,7%. Thus, vitamin B1 levels in blood, transketolase activity and the thiamine pyrophosphate effect in the hemolysate are useful biochemical indices for the diagnosis of beriberi. Above all, the thiamine pyrophosphate effect proved to be the most effective parameter in distinguishing the beriberi group from normal subjects.