When 5α-bromo-6, 19-oxidocholestanol acetate was exposed to CSD-10(ATCC: 19170) in nutrient broth, a substantial amount of 5α-bromo-6, 19-oxidoisoandrosterone was accumulated. This finding is controversial to the accumulation of 6, 19oxidoandrost-4-ene-3, 17-dione from 5α-chloro-6,19-oxidocholestanol acetate by the same organism. In order to clarify the effect of 5a-halogens on 3,8-hydroxy group oxidation, 5α-fluoro-6, 19-oxidocholestanol acetate was synthesized, and the oxidation pattern of 5α-halo-6, 19-oxidocholestanol acetates to 17-ketosteroids was studied. 5α-Bromo-6, 19-oxidoisoandrosterone seems to be an ideal intermediate to synthesize C-17-derivatized 19-norsteroids.