The occurrence of pigment and cholesterol calculi was studied in 45 patients with concrements in the gallbladder but no calculi in the common or intrahepatic bile ducts. Twenty-one of the patients had juxtapapillary duodenal diverticula diagnosed by duodenoscopy. Twenty-four patients had no diverticula. The classification of the calculi as pigment stones or cholesterol stones was based on quantitative determination of the cholesterol contents. Calculi with a cholesterol content of less than 25% were classified as pigment stones; calculi with a cholesterol content of more than 25% were classified as cholesterol stones. All pigment stones had a cholesterol content of less than 20%. With the exception of four patients the cholesterol content was over 70% in all cholesterol stones. Twelve of the 21 patients with were classified as pigment stones; calculi with a cholesterol content of more than 25% were classified as cholesterol stones. All pigment stones had a cholesterol content of less than 20%. With the exception of four patients the cholesterol content was over 70% in all cholesterol stones. Twelve of the 21 patients with were classified as pigment stones; calculi with a cholesterol content of more than 25% were classified as cholesterol stones. All pigment stones had a cholesterol content of less than 20%. With the exception of four patients the cholesterol content was over 70% in all cholesterol stones. Twelve of the 21 patients with diverticula had pigment stones, whereas only 1 of the 24 patients without diverticula had pigment calculi, a difference that was statistically significant (p less than 0.01).