Aim: The hydroxytyrosol (HT) and L-arginine methyl ester (L-NAME) effects were studied on electrically evoked contractions in human colonic circular muscle. The HT effect was also tested on electrophysiological parameters of stimulated colonic mucosa in buffer with/without Ca²⁺. Methods: Segments of colon were obtained from 12 patients (mean age73 yrs, range 63-89 yrs), undergoing left hemicolectomy. Motility: Strips (15x3mm) were mounted isometrically in an organ bath. Strips were exposed to electrical field stimulation (EFS) and the following drugs were tested: atropine (ATR) (2mM), guanethidine (GUA) (5mM), HT (200mM) or L-NAME (200mM). Permeability: Mucosa was mounted in Ussing chambers. Vt, Icc and Rt were recorded in resting condition and under stimulation with carbachol (100mM), forskolin and IBMX in the presence/absence of HT (100mM) in normal and Ca-free Krebs. Results: HT decreased electrically evoked contractions in the presence of ATR and GUA alone, and with L-NAME (p<0.05 - p<0.001). L-NAME increases electrically evoked contractions in the presence of ATR and GUA alone and with HT (p<0.05 - p<0.001). The HT, on the stimulated mucosa, produced a reduction of the Vt and Icc in control and in the buffer basolateral Ca-free (p<0.05 - p<0.001). The Rt is reduced with all buffer, except that in the control (p<0.05, p<0.01). Conclusions: HT seems to have an antioxidant effect, peroxynitrite dependent. Moreover it could also improve the alterated intestinal motility.