Calorie-reduced yogurts that were fortified with 1.32% oat fiber were prepared from lactosehydrolyzed milk, alone and supplemented with 2 and 4% sucrose or with 1.6, 3.6, and 5.5% fructose. Treated samples were compared with unsweetened yogurt and with yogurts sweetened with 2, 4, and 6% sucrose. Addition of 5.5% fructose increased fermentation time by 60%, slowing down the production of lactic, pyruvic, acetic, and propionic acids and the consumption of hippuric and orotic acids. Lactose hydrolysis had an inhibitory effect on starter activity at the beginning of fermentation and a stimulatory effect at the end of fermentation. Fiber addition led to increases in concentrations of acetic and propionic acid. Lactobacilli counts were lower in samples treated with fructose. The use of hydrolyzed milk had a stimulatory effect on total bacteria and lactobacilli counts throughout the cold storage period. After 28 d of storage, lactobacilli counts were consistently higher in fiber-fortified yogurts, but total bacteria counts were lower. Apparent viscosity increased with the addition of sweetener and fiber. Lactose-hydrolyzed and fructose yogurts had the highest viscosity values. Samples sweetened with sucrose received the highest scores for flavor. Fiber addition decreased overall flavor quality. The lactose-hydrolyzed yogurts received the highest flavor scores, independent of fiber fortification. Fiber addition improved the body and texture of unsweetened yogurts but lowered overall scores for body and texture in yogurts sweetened with sucrose.Funding for this project was provided by Dairy Management Inc. and a scholarship from the North Atlantic Treaty Organization (NATO) to support E. Fernández-García.Peer reviewed