1. Responses of single ganglion cells in the isolated rat superior cervical ganglion to gamma‐aminobutyric acid (GABA) applied via the bathing medium were recorded using intracellular micro‐electrodes. 2. GABA produced a large fall in cell input resistance, frequently to immeasurable levels. In thirteen cells showing a modest response to 100 muM GABA, input resistance fell from 50–5 +/−9–5 to 15.9 +/− 3‐2 Momega (means +/− S.E. of mean). After correction for resistance leaks introduced by the impaling electrode, the resting membrane resistance Rm and the resistance of the GABA‐shunt Rg in these cells were calculated to be 79–3 +/− 16–6 and 35–0 +/− 9–5 Momega respectively. 3. Cells with recorded resting membrane potentials greater than −42 mV were depolarized by GABA; at resting potential less than −42 mV they were hyperpolarized...