A trial was conducted to evaluate whether the addition of commercial enzyme preparations containing carbohydrases and a protease would increase the available metabolizable energy (ME) of maize-soya-based broiler diets. Seven thousand five hundred and sixty (7560) day-old Ross 788 chicks were randomly allocated to 60 pens (126 chicks per pen). The trial consisted of five dietary treatments, with 12 replicates per treatment. A negative control feed and three treatment feeds were formulated to contain a lower level of ME than a standard (positive control) feed. Two commercial enzyme preparations, one a mixture of amylase, xylanase and protease; and the other a β-mannanase product, were added separately or in combination to the treatment diets. Broiler performance was recorded over a 35-day period. Broilers fed the lower energy (negative control) diet performed significantly worse than all other treatments in terms of growth and feed conversion, but not mortality. The addition of the enzyme preparations to the energy-restricted diets significantly improved performance. Cumulative feed conversion ratio (FCR) on day 35 for the negative control birds was 12% higher than that of the positive control, while diets supplemented with single enzyme preparations resulted in 2.4% and 3.0% higher FCRs, respectively. Combining the two products caused significantly higher bodyweights and feed intakes than the positive control, while cumulative FCR was only 1.2% higher than for the positive control. A positive synergistic effect was evident when combining the two enzyme products. Performance gains in the enzyme-supplemented broilers were most pronounced during early growth.