It was shown that on reaction with arylsulfur trifluoride steroidal alcohols were converted into the corresponding fluorides with inversion of configuration,thus 3α-and 3β-cholestanols were converted into 3β-and 3α-fluorocholestanes respectively; whereas cholesterol was converted into 3β-fluoro-Δ⁵-cholestene,indicating homoallylio participation of the Δ⁵-double bond during the displacement reaction.Various reaction byproducts were isolated and identified,For ezample,from the reaction with cholestanols,Δ²-cholestene,the elimination prodnot was isolated; from the reaction with cholesterol,Δ^3,5-cholestadiene,the elimination product,dioholesteryl ether,the bimolecular dehydration product,and 3β-chloro-Δ⁵-oholestene,the product formed through the participation of the solvent CCl₄,were isolated.With Zrnitrophenyl sulfur trifluoride as fluorinating agent,a small amount of Δ⁴-holestenone-3 was also obtained.The influence of solvent and reaction temperature on the product distribution was described.