PbO2 was electrodeposited 40 min, 1 A/dm(2), from a HNO3-Cu(NO3)(2)-PbNO3 soln. on a 13-cm(2) 45-pore/in. reticulated vitreous C (RVC) anode. Aq. 0.04 M NaIO3 was oxidized 25250 min on the anode in 0.05, 0.125 or 0.5 M K2SO4 or 0.1, 0.25 or 1.0 M KOH or (A) 0.1 M KOH/0.5 M H2SO4 Current efficiencies rose with H2SO4 concn., 7, 13, 25%, and also with KOH concn., 31, 30, 44%, presumably on account of catholyte's cond., as borne out by the A-case rise to > 40%.