A dimensionless analysis for the limiting current in normal pulse polarography (NPP) with reactant adsorption obeying the Langmuir and the Frumkin isotherms is presented. Zone diagrams, calculated numerically with reference to limiting cases which can be approached by analytical expressions, allow the determination of the adsorption parameters. Conclusions concerning the initial accumulation of the adsorbate at zero current, apply to other voltammetries.