Classification of Ion-Selective Electrodes.- Natural and Synthetic Neutral Carriers for Membrane Electrodes.- Liquid Membrane Electrodes Based on Neutral Carriers.- Potentiometric Measurements of Ion Activities with Neutral Carrier-Based Electrodes.- Construction of Liquid Membrane Microelectrodes.- Use of Neutral Carrier-Based Liquid Membrane Microelectrodes.- General Aspects of Intracellular Measurements of Ions.- Neutral Carrier-Based Liquid Membrane Microelectrodes.- Impact of Neutral Carrier Microelectrodes.- References.