Control of fire was apparently acquired rather late in the course of hominid evolution. It is therefore necessary, in the study of dietary selection by early hominids, to consider the range of plants that would have proven inedible without cooking. Some plants contain toxins or digestibility-reducing compounds, and some plant constituents are indigestible. Cooking mitigates the impact of toxins and renders complex carbohydrates more digestible. Plant foods high in cellulose and/or starch are not readily digestible uncooked, and these constituents reduce the digestibility of other nutrients. Since nutrient intake is limited by the amount of food that can be processed per unit time, non-fire-using hominids should have attempted to increase nutrient intake by minimizing intake of these carbohydrates. Unlike animal sources of protein, plant materials generally lack a full complement of amino acids, and a variety of such materials must be ingested to obtain a balance of essential amino acids. Leaves and legumes, both possible sources of essential amino acids, may be ruled out as major suppliers of them for non-fire-using hominids-leaves because of their cellulose content and legumes because of their high frequency of toxic compounds. The limitations on the availability of plant protein strengthen the inference that some animal protein was ingested by early hominids on a regular basis. A ranking of plant parts as potential foodstuffs for non-fire-using hominids is proposed. When considered in conjunction with ecological factors, such a ranking should be helpful in generating models of hominid dietary selection before fire.