Screening studies for microbial transformation products of stemodin  have identified a number of microbial metabolites. Scale-up fermentation with Rhizopus arrhizus ATCC 11145 and Streptomyces sp. NRRL 5691 have resulted in the production of five metabolites that have been characterized with the use of 2D nmr and X-ray techniques. These metabolites have been identified as 18-hydroxystemodin , 16,18-dihydroxystemodin , 8β-hydroxystemodin , 8β, 18-dihydroxystemodin , and 7β,8β-dihydroxystemodin . The antiviral activity and cytotoxicity of the isolated metabolites have been evaluated.