The Symposium on "Ion Selective Microelectrodes and Their Use in Excitable Tissues" was held in Prague from July 8-11, 1980. It was organized by the Institute of Physiology of the Czechoslovak Academy of Sciences as a satellite symposium of the XXVIII Interna tional Congress of Physiological Sciences in Budapest. Sixty parti cipants met for three days in the historical setting of the Strahov Monastery. The informal and relaxed atmosphere of the scientific sessions, together with the social programme made the meeting a success and helped to cement old friendships and to form new ones. The organizers were happy to welcome as participants representatives from most of the laboratories working with ion-selective microelectrodes (ISMs) in the world. Neurophysiological research with liquid ion-exchanger ISMs in the Prague laboratory was started as early as 1971 due to the fact that one of us (P. H. ) had the opportunity of learning the technique directly from Dr. J. L. Walker in Salt Lake City. It was thanks to his patience and, later, his courtesy in providing us with the liquid ion-exchanger for potassium and silicone that we were able to get a start in what turned out to be, in a year or so, very strong international competition. This volume contains the papers presented at the Symposium. It is divided according to the actual sessions with names of the chair men, who helped the organizers to make the Symposium a real success.