Variation in the distribution of dietary nitrogen among the different amino acids is one factor that can modify the calorie equivalent per weight of amino acid or protein. This is important to consider when experimental diets with different amino acid compositions are compared and when indirect calorimetry is used to determine substrate oxidation rates. We developed a computer program to compute the energy content, oxygen equivalent, and respiratory quotient for arbitrary mixtures of amino acids and representative carbohydrates and fats. The calorie content of individual free amino acids was calculated by correction of the heat of combustion for the incomplete oxidation of amino acids characteristic of humans. Although these computations were presented before, we now report the limit of applicability of published values and the availability of the computer program to do these calculations.