Retinoic acid [1] and its analogues (retinoids) have recently generated interest as possible chemopreventive agents, but 1 is rapidly metabolized to many known as well as unknown products. Recently, microbial models have been employed for the study of mammalian metabolism. In this study two fungi, Aspergillus niger ATCC 16888 and Cunninghamella blakesleeana ATCC 8688a, were found to biotransform beta-ionone [2] and alpha-ionone [8] and may serve as models for the mammalian metabolism of retinoic acids. A. niger yielded oxidized metabolites, whereas C. blakesleeana gave products most of which were both oxidized and reduced. Methods developed here should prove amenable to studies utilizing 1 as the substrate for biotransformation.