This study investigated the composition of common duct gall stones from 61 patients, aged 49-94. The stones were collected endoscopically with a dormia basket after endoscopic papillotomy. The cholesterol content was measured both by infrared spectroscopy (mean 29%, range 0-99%) and enzymatically (mean 23%, range 0-96%). The results of the two measurements showed good correlation (r2 = 0.92), indicating that cholesterol can be adequately measured enzymatically. Most of the stones were pigment stones. When examined by infrared spectroscopy, 44 stones (72%) contained less than 50% cholesterol (mean 4%, range 0-23%). The bilirubinate content in these stones was 56%, range 12-100%. Forty two of these stones were brown stones, and only two were black stones. Pigment stones were associated with juxtapapillary diverticula (p < 0.01). It was found that brown pigment stones were the commonest symptomatic bile duct calculi in the patients studied, who are representative of a Western population.