Dextranase from the fungus Penicillium minioluteum hydrolyses alpha-1,6-glycosidic bonds in dextran polymers. The enzyme has been expressed in Pichia pastoris in the presence of selenomethionine (SeMet). The level of SeMet incorporation was estimated by amino-acid analysis to be 50%. The protein has been crystallized in space group P2(1)2(1)2, with unit-cell parameters a = 103.6, b = 115.3, c = 49.8 A and one molecule per asymmetric unit. The crystals diffract to 2.0 A and the presence of SeMet in the crystals has been confirmed by an X-ray absorption spectrum.