The addition of cholic acid to growing cultures of Eubacterium species V.P.I. 12708 caused a 25 and 46-fold increase in 7 alpha-dehydroxylation activity using cell extracts or whole cell suspensions, respectively. Bile acid conversion rates using either [14C]-cholic acid or [14C]-chenodeoxycholic acid as substrates increased at approximately the same rate when either cholic or chenodeoxycholic acid was added to growing cultures as inducer. The induction of 7 alpha-dehydroxylase activity was highly specific requiring a free C-24-carboxyl group and an unhindered 7 alpha-hydroxy group on the B ring of the steroid nucleus. Unexpectedly, cholic acid also rapidly induced NADH:flavin oxidoreductase activity in growing cultures of this bacterium.