A solid state polyvinyl chloride (PVC) membrane Li+-selective electrode was prepared and used as a detector in a low-dead volume flow through cell for the determination of Li+ in pharmaceutical formulations and human serum samples. The potentiometric performance characteristics of the electrode were calculated under the optimized flow conditions. The electrode had near-Nernstian behavior in the concentration range of 0.1-100 mM (R (2) = 0.9981) with a slope of 61.34 mV decade(-1) and detection limit of 0.080 mM. The relative standard deviation of the electrode response for eight replicate measurements of 100, 10, and 1 mM Li+ was 0.43%, 0.45%, and 0.99%, respectively. The designed flow-through cell detector system revealed sampling rates of approximately 70 injections per hour. Flow injection potentiometry (FIP) results obtained for the pharmaceutical formulations were in good harmony with the atomic emission spectrophotometry results. However, the electrode could not be used successfully for the direct analysis of real serum samples in FIP.