A suituable choice of supporting electrolyte medium for trace level determinations of chromium(VI) by differential pulse polarography is described. A comparative study suggests that sodium borate buffer is superior to ammonium acetate, ammonium tartrate, and especially to NaF which was recently known to be one of the most proper medium for the purpose. With 0.01 M borate, the best combination of high sensitivity, well-defined base line, and freedom from common interferents was attained. With $5.0{ imes}10^{-7}$M Cr(VI), tenfold excesses of Cu(II) and Fe(III), and a five hundred-fold excess of $Cl^-$ do not change the peak current by more than about 1%. And the detection limit was $5.0{ imes}10^{-8}$M Cr(VI).