The diets of five large mammalian herbivores in the Pare National des Volcans, a tropical montane forest, were determined using microhistological analysis of faecal material. Correction factors were used to calculate the biomass intake from the relative areas of leaf cuticle found in the faeces. Dietary nitrogen was calculated from the biomass intake obtained in the faecal analysis. This compared well with faecal nitrogen values corrected for dietary intake using equations from the literature. Both measures indicated that each of the five herbivores was obtaining a nitrogen-rich diet. Preferences for food plants were calculated using Manly's alpha as a measure. Nutrient content and other measures of dietary quality of the plants were determined and a multiple regression analysis used to determine which were important for the dietary intake of each herbivore. Mountain gorillas showed a selection of digestible food plants whilst buffalo selected food plants that were not easily digested. Other than in vitro digestibility, none of the measures of dietary quality correlated with the intake of the herbivores. Dietary overlap between the species was significantly lower than expected overlap values calculated using Monte Carlo analyses of neutral models. It is suggested that nutrients were not limiting the populations of these five herbivores.