Two infants under 3 mo of age who presented with obstructive jaundice secondary to cholelithiasis are reported. Neither infant had any congenital anatomic abnormality of the biliary tract leading to stasis, yet both had cultures of gallbladder bile that grew abundant bacteria. In both, recovery of gallbladder bile and sludge or actual stones allowed a detailed analysis of bile and stone composition. Bile was not saturated with cholesterol. In both cases, unconjugated bilirubin accounted for a large percentage of the total bile biliary pigments measured, and stercobilin was present in gallbladder bile. Bile beta-glucuronidase activity was higher when measured at the optimal pH of bacterial rather than tissue beta-glucuronidase. Analysis of stone morphology and composition showed characteristics of brown pigment gallstones with a layered appearance and the presence of calcium palmitate. This is the first report of detailed bile and stone analysis in infants and supports the hypothesis that brown pigment gallstones form spontaneously in infants who have bacterial infections in the biliary tract.