Thirteen feed ingredients, representative of those used in the feeding of poultry and pigs in South Africa, were assayed for apparent and true metabolizable energy content (AME and TME), with at least 60 determinations being made on each ingredient. The method used was that proposed by Sibbald (1976a). A second series of investigations revealed; that a 24 h collection period was not sufficient for the complete clearance of the ingredients fed and consequently a 48 h collection period was recommended; that errors are increased when either small or large amounts of feed are given by intubation, the ideal amount being closer to 0,015 of body mass (50 g/bird) than the 0,01 recommended originally by Sibbald (1976a); that age, body-mass and environmental temperature, do not influence EEL significantly; and that the TME is not increased by improving the protein quality of a feed ingredient.