The properties of crude and purified alpha-galactosidase formed by a strain of Aspergillus niger on wheat and rice bran-based media were examined. Cell-free extracts from both media had optimal a-galactosidase activities at 50 degrees C and pH 5.0. The crude preparation from wheat bran had the highest activity (0.13 U ml(-1)), whereas that from rice bran had a lower activity (0.08 U ml(-1)) but was more stable over a wider range of temperature and pH. Three peaks of activity occurred after dialysis and chromatography on Sephadex G-100, indicating the presence of multimolecular forms. The specific activity of the pure enzyme solution is 1567 U mu g protein(-1), and the protein responsible for the highest activity peak consists of two subunits with relative molecular masses of 78 and 69 KDa, respectively. The crude preparation simultaneously hydrolyzed stachyose and raffinose in two cowpea meal fractions (particle size <300 and <850 mu m) Raffinose was hydrolyzed 1.7 times faster than stachyose.