It has been shown that electrochemical cells comprised of a wettable, partially exposed, electrode, electrolyte, and a completely immersed counter electrode can be made sensitive to either ionizable or non-ionizable vapors (vapors which ionize or remain unionized in the cell electrolyte) by the judicious choice of electrode material and cell electrolyte. This type of electrochemical cell is particularly sensitive because the use of an exposed electrode with gas/liquid and liquid/solid interfaces allows an electroactive component of the gas phase to be brought to reaction at an electrode without prior dissolution in the bulk solution. The investigation of the absorption-induced electrode potential was undertaken in order to study the mechanism of the phenomenon and to determine the contribution of the electrolyte meniscus to the current and potential response of the AIEP cells. The current produced by an ionizable vapor (hydrogen chloride) injected into the gas stream entering a cell comprised of a partially exposed Ag/AgCl blade, aqueous hydrochloric acid electrolyte and an immersed Ag/AgCl wire counter electrode, has been investigated. The use of semi-silvered, sand-blasted, glass slides as the exposed electrodes has allowed us to probe the meniscus and film (formed on the exposed electrode) from bottom to top. With this probe, it has been shown that the response of this type of electrochemical cell can be attributed mainly to the upper part of the meniscus formed on the exposed electrode. In addition, the current also depended upon: (1) the volume of vapor injected, (2) the sign and magnitude of the external applied potential, and (3) the area of the exposed electrode covered by electrolyte.