Microbial dehydrogenations of resibufogenin (1) and cinobufagin (2) at 3-OH by Pseudomonas aeruginosa AS 1.860 were investigated. Four products were obtained, which were identified as 3-keto-resibufogenin (3), 3-keto-cinobufagin (4), 3-keto-deacetylcinobufagin (5) and deacetylcinobufagin (6) on the basis of their spectral data. When resibufogenin was added at 22 h and transformed for 2 h, a higher transformation rate was obtained. Compounds 4, 5 and 6 were metabolites of cinobufagin by human intestinal bacteria. (C) 2003 Elsevier Science Inc. All rights reserved.