The preparation of cholesteryl dihydrogen phosphate via chloesteryl phosphorodichloridate is described; although the reaction was successful for the preparation of ergosteryl and lanosteryl phosphorodichloridates, it failed with cholestanol and thiocholesterol. Dicholesteryl phosphorochloridate has been prepared but not diergosteryl or dilanosteryl phosphorochloridates. The hydrolysis of cholesteryl phosphorodichloridate has been examined. Reaction of thiophosphoryl chloride and cholesterol gave cholesteryl thionophosphorodichloridate but this could not be hydrolysed to the phosphate. Treatment of cholesterol with phosphorus pentasulphide gave OO-dichol-esteryl hydrogen phosphorodithioate contrary to previous reports. A study has been made of the decomposition of cholesteryl phosphorodichloridate in inert organic solvents.