Procedures for, and conditions during, inoculum collection and preparation, digestion, and residue recovery stages of the in vitro digestion technique were investigated to determine sources of within- and between-trial variability in digestion coeffkients for forages of different chemical composition. Digestion coefficients differed significantly among inoculum preparation times of 1, 2, and 4 hours and for a decline in rumen Buid temperature to 290 in transport. These differences were not uniform across forage species and did not correlate with forage digestibility. Digestion coefftcients differed significantly among inoculums prepared from fibrous deer rumen Bulds that were strained only, strained and layered, and blended ln a Waring blender and filtered through glass wool but did not differ between strained-layered and blendedfdtered inoculums of non-fibrous rumen fluid from a Astulated cow. Forage in vitro digestion in the absence of microbial activity (by solubility alone) indicated that forages having more soluble components were least affected by inoculums of different microbial activities, suggesting that between-trial differences be adjusted by a solubility, rather than a digestibility, factor. Inoculum nitrogen concentration did not correspond to between-trial differences in forage digestibility. Size of test tube, but not centrifugation versus filtration method of residue preparation, significantly affected digestion coefficients. However, because the standard large tube size cannot be centrifuged, the two methods of residue recovery would not be comparable unless the products of digestion were transferred from large tubes to centrifuge tubes. The end products of digestion must be stored under refrigeration if filtering proceeds for extended periods of time. Developing sound management policy for land use requires methods for quantitatively evaluating the capacities of habitats to support domestic ruminants and wildlife populations. Habitat evaluation, which includes animal forage preferences and nutritional values of those forages, is a first step in development of carrying capacity estimates to facilitate management decisions for species that are forage limited. The in vitro digestible dry matter (IVDDM) technique has been extensively used as an inexpensive and rapid method for large-scale evaluation of range forage quality (Pearson 1970, Johnson 1966). We have encountered difficulties applying this technique to large scale habitat evaluations for wild ruminants. These difficulties arise from problems associated with using wild ruminants as inoculum donors, both when comparing digestion coefficients from one in vitro trial with those from another trial and when preparing an’d handling the inoculum and the digested residues. Rumen microorganisms require a strictly anerobic environment, controlled temperature, and energy and nutrients for their survi