An experiment was designed to study the relative effectiveness of three external indicators in the determination of nutrient digestibility in burros. Eight mature male burros received Cr2O3 and polyethylene in their diet, and no restrictions were placed on their physical activity. Rectal “grab” fecal samples were collected for a 10-day period, pooled and analyzed for organic matter, crude fiber, crude protein, ether extract and nitrogen-free extract as well as the 2 indicators. Differences in digestion coefficients based on these indicators were not statistically significant. Subsequently, six fo the burros were confined in metabolism stalls and received daily doses of 144Ce in addition to the Cr2O3 and polyethylene. After a 10-day total collection period, samples were analyzed for the nutrients mentioned earlier and the 3 indicators. Differences between digestion coefficients based on polyethylene, 144Ce, and the total collection of feces were not statistically significant; those based on Cr2O3 were significantly (P < 0.05) lower. The low digestion coefficients based on Cr2O3 were directly attributed to the low recovery of this indicator. Recovery of Cr2O3 was 81.5% as compared with 96.6% and 103.2% of the 144Ce and polyethylene, respectively. Crude protein digestion was significantly decreased (P < 0.025), and ether extract digestion was significantly increased (P < 0.025), when the burros were in metabolism stalls.