To evaluate the usefulness of "single stool sample" analysis in the investigation of steatorrhoea instead of 72-h stool collection, we examined 57 stool samples of patients with cystic fibrosis (CF) while on pancreatic enzyme therapy and 29 stool samples of healthy children. We compared results of fat, nitrogen, water and energy content. Fat was determined by the method of Van de Kamer et al. and the Acid Steatocrit (AS) method, water by vacuum drying, nitrogen by the Dumas method and energy was obtained using a bomb calorimeter. Results (median) for CF patients and healthy controls were significantly different (P ≤0.0001) for fat respectively: 8.90 and 4.75/100 g wet weight (ww) stool as measured by the method of van de Kamer et al. and 28.6% and 7.2% by the AS method. Energy results for energy were also significantly (P ≤0.0001) different: 742.96 and 549.32 kJ/100 g ww stool for CF patients and healthy controls respectively. Results of single stool sample water and nitrogen were similar in both groups. These results were comparable to those of a 3-day stool collection, as reported in the literature. Conclusion: results from single stool samples yield clinically useful information concerning fat and energy. Single stool sample analysis is therefore useful for frequent monitoring of faecal fat and energy.