Objectives: Ether-a-go-go-related (ERG, Kv11) channels are a subfamily of voltage-gated K+ channels that have been recently identified in a number of phasic smooth muscle. However, little is known about the expression of Kv11 channels in non-phasic vascular smooth muscle. The present study investigates the expression, function and electrophysiology of Kv11.1 in murine carotid artery (mCA) and thoracic aorta (mTA). Methods: 6-8 week old BALB/c mice were sacrificed by cervical dislocation. The mPV, mCA and mTA were used in conventional and quantitative polymerase chain reaction (PCR), immunocytochemistry, Western blotting, electrophysiology and isometric tension recordings. Results: Quantitative PCR experiments showed expression of ERG1 in a variety of vascular preparations. ERG1a was the dominant splice variant in mCA and mTA, whereas ERG1b was more abundant in the mPV. Western blot confirmed the existence of Kv11.1 in tissue lysates and immuncytochemistry was able to localise Kv11.1 to the membrane domain. Compared to mPV, whole cell recordings from mCA cells did not exhibit the characteristic 'hooked' kinetics at hyperpolarised potentials, under external [K+] of 5, 35 and 140 mM. Kv11 channel activators PD118057 and NS1643 were unable to evoke IERG but did enhance the outward K+ current at +40 mV, which was paxilline-sensitive and dofetilide-insensitive. mCA and mTA segments precontracted with 1 mM phenylephrine and in the presence of 1 mM paxilline were relaxed after 120 minute incubation with PD118 (10 mM , ~80%) and NS1643 (10 mM, ~45%). Conclusion: This study has shown the presence of Kv11.1 in arterial smooth muscles that are functionally 'silent' compared to a spontaneously rhythmic vein (mPV).