Whole oat flour obtained by hammer milling was fermented with Lactobacillus plantarum along with white flour and bran in order to compare the suitability of these substrates for the production of a probiotic beverage. The three substrates show a viable cell concentration at the end of fermentation above the minimum required in a probiotic product. The highest cell concentration was observed in white flour (9.16 Log(10) CFU/mL) and the lowest in the bran sample (8.17 Log(10) CFU/mL). (c) 2008 Elsevier Ltd. All rights reserved.