A 4-hydroxy-3-methoxycinnamic acid (ferulic acid) esterase has been purified from the extracellular broth of cultures of Streptomyces olivochromogenes after growth on oat splet xylan. The purification procedure utilizes ion exchange on DEAE-BioGel A, anion exchange on Mono Q, gel filtration and hydrophobic interaction chromatography. The purified enzyme appeared as a single band on SDS-PAGE, with an apparent Mr of 29,000. Two bands, at pI7.9 and 8.5, were observed on isoelectric focusing. With methyl ferulate as substrate, the pH and temperature optima were 5.5 and 30 degrees C respectively, with a Km of 1.86 mM and Vmax of 0.3 mumols min-1 mg-1. The purfied enzyme released ferulic acid from de-starched wheat bran only in the presence of xylanase.