The title esters were prepd. by reaction of the 21,21-diiodo deriv. with H3PO4 or H2SO4 or their salts in acid soln. Thus, 21,21-diiodo-16.beta.-methyl-9.alpha.-fluoro-11.beta.,17.alpha.-dihydroxypregna-1,4-diene-3,20-dione was refluxed in aq. Me2CO contg. K2HPO4 and 85% H3PO4 for 3 hr to give 92.5% betamethasone 21-phosphate (I). Treating I with NaOH-MeOH (pH 10.5) led to the easily sol. di-Na salt.