Three series of digestibility experiments with mature geldings indicated no significant differences between the 4N-HCl insoluble ash indicator and the total collection methods for determination of apparent digestible nitrogen and digestible energy. There were significant differences (P < 0.05) between animals for the insoluble ash method in two of the three trials. No significant differences were found when the number of sampling days involved was reduced from 7 to 4 days and random grab samples of feces were used for insoluble ash determinations. Random grab samples taken for 1, 2, 3 or 4 days did not give significantly different digestion coefficients using the insoluble ash indicator method. Period differences in the insoluble ash method were observed when 3-day collections during five successive periods were taken from four individual geldings by the grab method. A study with four geldings during two test periods using cotton strips as indicators showed mean rate of passage of digesta to be 70.2 h. The overall results suggest that random grab fecal samples using the 4N-HCl insoluble ash method has potential for use in the determination of digestibility coefficients for horses.