Ionized calcium (Ca2+) and bicarbonate (HCO(3)-) are important ions for gallstone formation. In the present study the effect of indomethacin and vasoactive intestinal peptide-antiserum (VIP-antiserum) on the Ca2+, HCO(3)- and fluid secretion in the inflamed gallbladder were tested in a validated experimental model in cats. The animals were studied in acute experiments 6 weeks after cystic duct ligation and gallstone implantation. During basal conditions there was a continuous secretion of Ca2+, HCO(3)- and fluid into the lumen of the inflamed gallbladder. Indomethacin and VIP-antiserum inhibited the Ca2+, HCO(3)- and fluid secretion across the inflamed gallbladder mucosa. Intraluminal amiloride inhibited the absorption of Ca2+, HCO(3)- and fluid after indomethacin infusion. An impaired absorption of Ca2+, HCO(3)- and fluid in the inflamed gallbladder is probably important for the solubility of calcium salts in the early stages of inflammation in the gallbladder mucosa.