Two foods, distillers' wet draff and draff plus pot ale syrup, containing 207 and 256 g crude protein per kg dry matter respectively, were given as sole food at the maintenance level to four adult wether sheep. Two of the sheep were given draff and two draff plus syrup for a 28-day period; the treatments were then changed over for a second period. The copper contents of the foods were 17 and 30mg/kg dry matter for the draff and draff plus syrup respectively. Sheep are particularly susceptible to copper and care should be taken when feeding such by-products, but during these short-term trials there was no evidence of copper poisoning. Energy losses in the faeces and urine were measured for all sheep, and methane losses were measured in closed-circuit respiration chambers for two sheep on each treatment. The metabolizable energy values of the foods were 10·8 (s.e. 0·15) and 12·5 (s.e. 0·15) MJ/kg dry matter for the draff and draff plus syrup respectively. The proportions of gross energy intake lost as methane were 0·029 for the draff and 0·042 for the draff plus syrup; these were much lower than the values predicted by the commonly used equation.