The application of fibers from various sources in food production is increasing due to their beneficial effects on human health. The aim of this paper is to investigate the effects of non-modified and modified sugar-beet fibers on dough and bread yield, bread volume and bread crumb quality. Dry sugar-beet fibers were ground, sieved through a laboratory sieve and a fraction with particles less than 95 mu m was used for further treatment. It was hydrated for 24 h and pressed for removing excess water. In such a way, hydrated but non-modified fibers were obtained. Part of the non-modified fibers was exposed to a further treatment with H2O2, at the pH values: 3.5, 7 and 11 for the additional 24 h. Treated blends were neutralised, washed with tap and distilled water, pressed and blended to a homogenous mass with fine particles. In such a way modified fibers were obtained. Dough and bread were made from white flour, powdered vital gluten, salt and yeast (as it is used in regular bread production), without fibers, with non-modified fibers and with modified fibers. Experiments were planned so that the quantity of the applied fibers in the blends varied from 0% to 15%, while gluten quantity varied from 0% to 5%. Controlling characteristics of the product were: yield of dough and bread, volume, crumb quality. By applying the regression analysis method on the measured data, mathematical models for both fibers application were defined. Based on the experimental results as well as on the mathematical considerations following conclusions were drawn: increase of content of both fibers (non-modified and modified) increases yield of dough and bread but decreases volume of bread and bread crumb quality. On the other hand, increase of gluten quantity increases the volume of bread at small amounts of fibers; when fibers quantity increases, gluten proved ineffective. By the comparison of non-modified and modified fibers, the advantage is given to the non-modified fibers. An enrichment of bread with less than 10% of non-modified fibers, accompanied with a few percents of gluten, is highly recommended. (c) 2006 Elsevier Ltd. All rights reserved.