The intracellular beta-glucosidase from Kluyveromyces marxianus NBRC1777 (KmBglI) belongs to glycoside hydrolase family 3 and has a unique domain architecture. Selenomethionine-labelled KmBglI was purified and crystallized by the hanging-drop vapour-diffusion method using the purified enzyme at 30 mg ml(-1), 0.04 M potassium dihydrogen phosphate pH 5.1, 16%(w/v) PEG 8000 and 20%(v/v) glycerol. The crystal belonged to space group C2, with unit-cell parameters a = 245.8, b = 148.7, c = 119.9 angstrom, beta = 112.9 degrees. Multiple-wavelength anomalous dispersion data were collected at 2.4 and 2.5 angstrom resolution. A tetramer was assumed to be present in the asymmetric unit, which gave a Matthews coefficient of 2.6 angstrom(3) Da(-1).