Objective: The aim of this work was to determine if dysprosium chloride (DyCl3) is a suitable nonabsorbable marker for studies of labeled-triglyceride excretion in cystic fibrosis patients allowing excretion to be determined accurately after analysis of one or two stools. Methods: A series of 66 absorption studies were conducted in 36 young cystic fibrosis patients over a five year period. All tests consisted of ingesting a single test meal containing both 13C-labeled triglyceride (TG*) and DyCl3; in most studies the food colorant brilliant blue (FD&C blue #1) was administered along with the DyCl3. Ingestion of the test meal was followed by collection of individual stools for 72 to 96 hours. Stools were analyzed for 13C-Excess (13C*) and Dy. Results: Excretion of Dy in cystic fibrosis patients who exhibited a wide-range of steatorrhea was quantitative. Fractional excretion of Dy and 13C* in individual stools showed a high linear correlation (r2 = 0.969) with a slope and y-intercept close to unity and zero, respectively. As a result, estimates of TG* excretion based on analysis of only two stools (partial pool method, PPM) were not different from those based on the analysis of all stools or stool composites. This was true both when Dy content and when stool color due to ingested brilliant blue was used to determine which stools to analyze for the PPM. Conclusions: Combining the use of Dy and brilliant blue permits reasonably accurate estimates of fecal TG* excretion after analysis of samples from two easily identified stools. This practical method can be used to address many important clinical and experimental questions regarding triglyceride digestion and absorption that may otherwise go unanswered. © American 2003 College of Nutrition.