Peptide VIP is a vasodilator, bronchodilator and smooth muscle relaxant. Like PACAP, a closely related peptide, VIP is largely inhibitory in the gastrointestinal tract and its neuroprotective actions are mediated by the release of activity-dependent neurotrophic factors from glial cells. To characterize the effects of VIP on both contraction and relaxation of guinea pig gallbladder (GPGB) muscle, cumulative additions of VIP was performed with strips at basal tone or with strips pre-contracted with cholecystokinin-octapeptid, and VIP had no effect on basal tone.