Xyloglucan endotransglycosylases (XETs) cleave and religate xyloglucan polymers in plant cell walls. Recombinant XET from poplar has been purified from a Pichia pastoris expression system and crystallized. Two different crystal forms were obtained by vapour diffusion from potassium sodium tartrate and from an imidazole buffer using sodium acetate as a precipitant. Data were collected from these crystal forms to 3.5 and 2.1 A resolution, respectively. The first crystal form was found to belong to space group P3(1)21 or P3(2)21 (unit-cell parameters a = 98.6, b = 98.6, c = 98.5 A) and the second crystal form to space group P6(3) (unit-cell parameters a = 188.7, b = 188.7, c = 46.1 A).