We recently showed that acute ethanol inhibits contractility of the lower esophageal sphincter (LES) and the lower esophageal body (LEB) both in vivo and in vitro. To evaluate the mechanism of this inhibitory effect of ethanol, we investigated the role of nitric oxide (NO) on contractility of isolated LES and LEB circular muscle strips using inhibitors of NO synthase (NOS), NG-nitro-L-arginine methyl ester and NG-nitro-L-arginine. Ethanol significantly decreased LES basal tone. This effect was not mediated by NO, because inhibition was not prevented by inhibitors of NOS. Electrical field stimulation caused an On-response relaxation from LES strips, and an Off-response contraction from both LES and LEB strips. Inhibitors of NOS prevented the On-response relaxation of LES, but had no significant effect on LES Off-response contraction. Ethanol potentiated the On-response relaxation of the LES Off-response contraction. Ethanol potentiated the On-response relaxation of LES, but had no significant effect on Off-response contraction. Ethanol's potentiating effect of the On-response relaxation is NO-mediated, because it was abolished by NOS inhibitors. Ethanol also inhibited carbachol-induced LES contractility. This inhibitory affect was NO-mediated, because NOS inhibitors abolished it. Ethanol inhibited both the Off-response contraction and carbachol-induced contraction of LEB strips. These effects were not NO-mediated, because they were not affected by NOS inhibitor. These data suggest that NO is not a mediator for the inhibitory effect of ethanol on LEB contractility, and that NO seems to be a mediator of ethanol inhibition of some aspects of LES motor functions.