A probe for amperometric measurement of dissolved hydrogen dissolved in a liq. contains an Pt indicating electrode and a metallic pseudoref. electrode, constituted of, preferably, Ag or Hg, with a deposit of oxide on the pseudoref. electrode, preferably, Ag2O or AgO. The probe is filled with a neutral or basic electrolyte soln. nonsusceptible to deactivating the indicating electrode or undergoing an electro-oxidn., such as solns. of KOH or K2SO4. The hydrogen probe can be realized from a Clark-type oxygen probe. [on SciFinder (R)]