The microdialysis technique was used to study the effect of nitric oxide synthase (NOS) activity on taurine release. Taurine release was characterized in rat striatum that was excitotoxically lesioned compared to normal conditions. The basal taurine level of the dialysate decreased during quinolinate (QUIN) lesion in parallel to the cell degeneration process. The K+-stimulated taurine concentration also decreased during QUIN-lesion, but to an extent that was different from that of basal values. K+-stimulated taurine levels were further markedly lowered by coapplication of the NOS inhibitor L-NAME in control and in lesioned animals up to 30 days after QUIN-injection. Postdegenerative tissue did not show any NOS-dependency in K+-induced taurine release. We conclude that a substantial part of K+-induced taurine release depends on NOS-activity both in normal brain tissue and in excitotoxically induced neurodegeneration. The main source of K+-induced taurine release in control rats are neurons but in lesioned animals are activated astroglial cells.