['We investigated the effects of aging on the contributions of NO and endothelium-dependent hyperpolarization (EDH) to endothelium-dependent relaxation in saphenous arteries of male and female C57BL/6J mice aged 12, 34 and 64 weeks.', 'Vasomotor responses of saphenous arteries were analysed by wire myography in the absence and presence of stimuli of the endothelium, inhibitors of NOS, and inhibitors and stimulants of small (KCa 2.3) and intermediate (KCa 3.1) conductance calcium-activated potassium channels.', 'Arterial relaxing responses to sodium nitroprusside and to ACh in the absence of pharmacological inhibitors (indomethacin and L-NAME), were similar in all age groups and sexes, but those mediated by endothelium-derived NO were slightly but significantly increased in 64-week-old male mice. In the presence of inhibitors, 12-week-old animals showed pronounced ACh-induced relaxation, which was significantly reduced in 34- and 64-week-old mice of both sexes. The EDH-related component of ACh-induced relaxations was abolished by TRAM-34 (KCa 3.1 blocker) or UCL 1684 (KCa 2.3 blocker). Although the maximal relaxation induced by NS309 (KCa activator) was not affected by aging, the sensitivity for NS309 significantly decreased with aging. The presence of SKA-31 (KCa modulator) potentiated relaxations induced by ACh in arteries of 12-week-old but not older mice.'] Do endothelium-dependent hyperpolarization-related relaxations diminish with age in murine saphenous arteries of both sexes?