The degradation of aflatoxin B1 by various representatives of bacteria, yeasts and moulds in growing and resting cultures was investigated. We found that growing cultures of Corynebacterium rubrum degraded the added aflatoxin nearly quantitatively. -- Growing cultures of anascosporogenous yeasts degraded most of aflatoxin B1 while no degradation of this substance by ascosporogenous yeasts could be stated. Moulds degraded aflatoxin B1 to a high extent. -- With regard to the course of degradation three types can be distinguished. -- In the cultures of moulds two blue fluorescing compounds were found beside aflatoxin B1.