Cortical application of crystalline KCl in male cats anaesthetised with alpha-chloralose induced four transient negative deflections in cortical direct current (d.c.) potential. In vehicle treated animals d.c. shifts were associated with a hyperaemia and a multiphasic nitric oxide (NO) release. In these animals, the first negative shift in d.c. potential produced a significantly larger NO electrode current, when compared to subsequent cortical depolarisations. However, regional cerebrovascular laser Doppler flux (rCBF[LDF]) increases were similar for each event. In L-N(G)-nitro-L-arginine (L-NAME; 10 mg/kg i.v. infused over 30 min) treated animals, d.c. shifts were also associated with NO release following a multiphasic waveform and increase in rCBF(LDF), but were significantly attenuated when compared to controls.