The partial enzymatic hydrolysis of chicory inulin (GFn; 2 < or =n < or =60) yields an oligofructose preparation that is composed of both GFn-type and Fn-type oligosaccharides (2 < or =n < or =7; 2 < or =m < or =7), where G is glucose, F is fructose, and n is the number of beta(2-->1) bound fructose moieties. Human studies have shown that feeding GFn-type oligomers significantly modifies the composition of the fecal microflora especially by increasing the number of bifidobacteria. The experiments reported here were used to test the hypothesis that the Fn-type molecules have the same property. During a controlled feeding study, 8 volunteers (5 females and 3 males) consumed 8 g/d of an Fn-rich product for up to 5 wk. Fecal samples were collected and analyzed for total anaerobes, bifidobacteria, lactobacilli, bacteroides, coliforms and Clostridium perfringens. Both 2 and 5 wk of oligofructose feeding resulted in a selective increase in bifidobacteria (P<0.01). In addition, a daily intake of 8 g of the Fn-type oligofructose preparation reduced fecal pH and caused little intestinal discomfort.