Streptomyces avermitilis CECT 3339 is grown on Brewer's spent grain (BSG) and the production of feruloyl esterase (FAE) and (1 --> 4)-beta-D-xylan xilanohydrolase (xylanase) activities is studied over 5 days. Maximum level of xylanases was found at day 1. FAE activity on methyl ferulate reached a maximum level at day 2, whereas FAE activity on feruloylated oligosaccharides, either from wheat bran or sugar-beet pulp, was maximal at day 1. The cultures (1-5 days) from S. avermilitis CECT 3339 grown on BSG and on other two agro-industrial residues such as de-starched wheat bran and sugar-beet pulp were tested for the release of hydroxycinnamic acids (ferulic and p-coumaric acids) from BSG. Most ferulic acid (FA) was released when culture supernatants from day 1 and BSG as carbon source (43% of total alkali-extractable ferulic acid) and from day 2 and de-starched wheat bran as carbon source (41.2%) were used. The level of p-coumaric released in all cases was lower (<9% of total alkali-extractable p-coumaric acid; pCA). The importance of the time of growth for the enzyme production involved in the hydrolysis of BSG is discussed.