The absorption of oral 14C-glyceryl tripalmitate was tested in 77 subjects by hourly interval sampling of breath 14CO2 for up to 6 h. A highly significant correlation was obtained between maximum breath 14CO2 activity and faecal fat excretion. The test was very effective in differentiating between patients with and without steatorrhoea. Repetition of this examination with oral 14C-palmitic acid demonstrated normal absorption in pancreatic steatorrhoea but impaired absorption in intestinal steatorrhoea, thus enabling these conditions to be distinguished. The 14C breath tests are most useful as simple and inexpensive outpatient screening tests for steatorrhoea.