The Probe Beam Deflection (PBD) together with cyclic voltammetry and chronoamperometry have been used to study in-situ an electrocatalytic reaction : the hypophosphite ion electro-oxidation on the nickel electrode in the alkaline medium. The results are discussed in terms of a previously proposed mechanism and are consistent with the involvement of a non faradaic rate determining reaction preceding the oxidation step. The high sensitivity of the technique allows an accurate evaluation of the catalytic activity of slightly modified surfaces. Despite the non catalytic activity exhibited by the beta-Ni(OH)(2) on the cyclic voltammetry, the PBD reveals its capability to oxidize the hypophosphite ion.