WHOLE-CELL recordings in rat olfactory bulb slices showed that bath application of 5 mM taurine produces a potent and reversible inhibition of identified mitral and tufted cells. Under current-clamp conditions, a shift of the membrane potential toward the chloride equilibrium potential and a 75% reduction in the membrane resistance were observed. These effects were strongly blocked by bicuculline (10 μM), but not by GABABantagonist and strychnine, and completely maintained under the blockage of synaptic transmission. The results suggest that inhibition of bulbar relay neurons produced by taurine is primarily due to direct activation of somatic GABAAreceptors and initiation of chloride conductance. This study demonstrates for the first time the actions of taurine in the olfactory system.