In this work, the influence of phosphate buffer and proteins on the potentiometric response of a polymeric membrane-based solid-contact Pb²⁺-selective electrode (Pb²⁺-ISE) was studied. The effects of bovine serum albumin (BSA) adsorption at the surface of the ion-selective membrane combined with electrode conditioning in phosphate-buffered saline (PBS) solution was elucidated by potentiometry and electrochemical impedance spectroscopy. The adsorbed BSA at the surface of the Pb²⁺-ISE slightly lowered the detection limit but did not influence the selectivity of the Pb²⁺-ISE towards the interfering ions studied (Cu²⁺, Cd²⁺). Conditioning of the Pb²⁺-ISE in 0.01 mol dm^–3 PBS resulted in a super-Nernstian response which was related to fixation/extraction of Pb²⁺ in the ion-selective membrane via precipitation of Pb₃(PO₄)₂ by PO₄^3– anions present in PBS. By conditioning of the Pb²⁺-ISE in 0.01 mol dm^–3 PBS + 1 mg/ml BSA it was possible to extend the linear response range of the Pb²⁺-ISE towards lower analyte concentrations. The utilization of this conditioning procedure was validated by determination of Pb²⁺ concentrations down to ca 20 ppb in aqueous samples by Pb²⁺-ISEs and by comparing the results with those obtained by ICP-MS.