Abstract Although contraction of the rat stomach fundus by 5-HT is known to be mediated by the 5-HT2B receptor, the second messenger pathways involved in this response remain unclear. Since nitric oxide (NO) has been associated with contraction of certain gastrointestinal smooth muscle, the purpose of this study was to determine if NO is involved in 5-HT-induced contraction in the rat stomach fundus. The arginine analogs L-NAME and L-NMMA, at a concentration (100 μM) established to inhibit NO synthase in the rat stomach fundus by inhibiting depolarizationinduced relaxation in this tissue, had no effect on 5-HT contraction. Furthermore, the NO donors sodium nitroprusside and SNAP did not contract rat stomach fundus under basal tone, whereas 5-HT was a potent contractile agonist. These data do not support a role for NO in 5-HT 2B receptormediated contraction in the rat stomach fundus.