The arachidonic acid metabolites are recognized as important biochemical mediators of inflammation in a wide variety of disease processes. Also the ability to change prostaglandin formation by inhibition of prostaglandin synthetase activity with aspirin and other nonsteroidal anti-inflammatory agents is important in the treatment of many diseases with an inflammatory component. Although gallbladder disease is primarily related to the development of cholesterol stones, inflammation is an important contributor to the subsequent symptoms and accompanying illness. This research evaluates the formation of prostaglandins E and F by gallbladder tissue. Gallbladder mucosal cells and muscle tissue were maintained in tissue culture medium. Production of prostaglandins E and F was determined by quantitation by radioimmunoassay of these substances in culture media and mucosal cell and muscle tissue homogenates. Prostaglandin production by normal gallbladder tissue in a variety of species including man was consistently demonstrated in the nanogram per milligram mucosal cell or muscle tissue protein range. In cats, inflammation was produced by placing a 4% carrageenan-soaked sponge in the gallbladder, and prostaglandin synthetase inhibition was produced by indomethacin administration. The feline gallbladder increased prostaglandin F production in inflamed gallbladder mucosal cells and E production by inflamed gallbladder muscle tissue, and indomethacin inhibited these increases. A positive, significant correlation existed between the increased prostaglandin E and prostaglandin F production by inflamed gallbladder tissue and the amount of inflammation present as determined by a histologic score. The histologic score of the amount of gallbladder inflammation present was decreased significantly by indomethacin when compared with inflamed gallbladders from cats not receiving indomethacin. Prostaglandins may play a role in the inflammatory processes occurring in acute cholecystitis.