The vit. B1 content of different parts of a number of plants from certain important botanical families, detd. by the thiochrome technique, compares favourably with available published figures. The vit. B1 content is highest in seeds; in most leaves it is a constant value of about 25 I.U. per 100 g., regardless of the botanical family. Variation in vit. B1 content of fruits of the Rosaceae may be due to degree of ripeness.