In a study of the effect of storage on the vitamin B6 activity of foods, the vitamin B6 content of different foods of plant and animal origin and also of a mixed feed with added pyridoxine were analyzed microbiologically using Saccharomyces carlsbergensis as test organism. Vitamin B6 activity was determined initially, in some of the specimens after storage for 10 months and again in all foods after 40 months. The storage period of 10 months caused a loss of the natural vitamin B6 content of about 25--30%. This loss increased to more than 50% after 40 months storage. The diet containing the high level of synthetic pyridoxine lost 85% of its vitamin B6 content.