A voltammetric study of proton reduction from aqueous solution of pyridoxal-5’-phosphate (PLP) is carried out at Pt microdisc electrodes. Steady-state waves for the reduction of the solvated proton and some acid forms of PLP are observed in the concentration interval investigated. The effect of the acid concentration, the electrode size and the influence of the supporting electrolyte on the limiting current, half-wave potential and shape of the wave, are analyzed in view of theoretical predictions for strong and weak polyproptic acids.