Abstract  The composition of pigment gallstones from patients with and without cirrhosis was compared. Carbonate-containing pigment stones were distinguished from noncarbonate stones by infrared spectroscopy. Calcium was the major cation of each stone group. The major anion in noncarbonate pigment stones was bilirubinate or phosphate, but was carbonate in carbonate stones. The composition of pigment stones from cirrhotic and noncirrhotic patients was similar except that significantly less carbonate was present in carbonate stones, and less pigment (bilirubinate) was present in noncarbonate stones from noncirrhotics. These data suggest that irrespective of the presence of cirrhosis, the formation of noncarbonate pigment stones involves the selective precipitation of calcium bilirubinate and phosphate, whereas carbonate stone formation involves the selective precipitation of calcium carbonate.