Objective: To determine the tolerance of increasing dosages of an incompletely hydrolysed and/or incompletely absorbed food dextrin coming from wheat starch, NUTRIOSE®FB, at daily levels of 10 and 15 g up to 60 and 80 g, respectively. Design: A randomized, double-blind, multiple dose, placebo-controlled, combined crossover and parallel trial. Setting: The metabolic ward of TNO Nutrition and Food Research. Subjects: A total of 20 healthy men (age 31.7±9.1 y; BMI 24.5±2.9 kg/m2). Intervention: One group of 10 subjects consumed on top of their diet 10, 30 and 60 g of NUTRIOSE®FB or maltodextrin (placebo) daily. The other group of 10 subjects consumed 15, 45 and 80 g daily. Each dose was consumed for 7 days. Results: Compared with placebo, flatulence occurred more frequently over the last 6 days on 30, 60 or 80 g/day of NUTRIOSE®FB (P<0.05). During the last 24 h, that is, days 6-7, of 60 and 80 g/day of NUTRIOSE®FB, the frequency of flatulence was even higher (P<0.05). During the last 24 h on a daily dose of 60 g NUTRIOSE®FB, the frequency of defecation decreased (P<0.05). Bloating occurred more often during the last 24 h on 80 g/day of NUTRIOSE®FB (P<0.05). None of the doses of NUTRIOSE®FB resulted in diarrhoea. Compared to baseline levels, breath H2 excretion, which was only measured after a week with 10 and 15 g of NUTRIOSE®FB daily, increased (P< 0.05). However, no difference in area under the curve was found. Conclusions: NUTRIOSE®FB is a fermentable carbohydrate and is well tolerated up to a dose of 45 g daily. Higher daily dosages (60 and 80 g) may result in flatulence, but does not result in diarrhoea. © 2004 Nature Publishing Group. All rights reserved.