The effect of changing dietary energy and crude fibre concentrations on the utilization of metabolizable energy (ME) was investigated in four growing ostrich chicks by addition of lucerne meal to a maize-lucerne based diet. The experiment was carried out in an indirect open circuit calorimeter. When ME concentration was lowered by 7.5%, cell wall digestibility decreased by 9% and energy metabolizability (ME/GE) by 15% (P < 0.05). Energy loss as methane was negligible and was not influenced by dietary energy or crude fibre concentration. Maintenance energy requirement was 0.44 MJ /W, kg0.75/day and the efficiency of ME utilization for growth was 0.32. The efficiency of ME utilization tended to deteriorate with decreasing energy or increasing crude fibre concentration in the diet. It was concluded that future research should be aimed at quantifying the influence of crude fibre on ME utilization over an extended range of dietary energy concentrations.