Solubilization and depolymerization of carbohydrates by treatment of orange peel with dilute (0.06 and 0.5%) sulfuric acid at 100, 120 and 140 degrees C has been investigated The acid treatments solubilized a large portion of total carbohydrates in orange peel. However, only soluble sugars and sugars derived from hydrolysis of hemicelluloses were efficiently released by the treatment with hot dilute sulfuric acid. Cellulose and segments of pectin containing galacturonic acid units were very resistant to acid-catalyzed hydrolysis. The treatment with dilute sulfuric acid had a positive effect on the rate of subsequent enzymatic hydrolysis of orange peel by a mixture of cellulolytic and pectinolytic enzymes.