Simultaneous measurements of fecal C-14 and expired 14CO2 in the breath are necessary to evaluate patients with various ileal abnormalities and bile salt malabsorption. Following the oral ingestion of the labeled bile acid, glycine-[I-14C]cholic acid, detection of increased fecal C-14 without abnormal expiration of 14CO2 identifies patients with ileal resection. This contrasts with the normal fecal C-14 content and abnormal expired 14CO2 found in patients with bacterial overgrowth. Fecal C-14 content was determined by utilizing Van Slyke combustion of the specimen and trapping the liberated 14CO2 with Scintisorb C. The method is simple, rapid, and accurate, and expands the diagnostic usefulness of the bile salt absorption test.