Approximately 1 million metric tons of grapefruit were processed in the 2003/04 season resulting in 500,000 metric tons of peel waste. Grapefruit peel waste is usually dried, pelletized, and sold as a low-value cattle feed. This study tested different loadings of commercial cellulase and pectinase enzymes and pH levels to hydrolyze grapefruit peel waste to produce sugars. Pectinase and cellulase loadings of 0, 1, 2, 5, and 10 mg protein/g peel dry matter were tested at 45 degrees C. Hydrolyses were supplemented with 2.1 mg beta-glucosidase protein/g peel dry matter. Five mg pectinase/g peel dry matter and 2 mg cellulase/g peel dry matter were the lowest loadings to yield the most glucose. Optimum pH was 4.8. Cellulose, pectin, and hemicellulose in grapefruit peel waste can be hydrolyzed by pectinase and cellulase enzymes to monomer sugars, which can then be used by microorganisms to produce ethanol and other fermentation products. (c) 2006 Elsevier Ltd. All rights reserved.