Single crystals of a multienzyme complex isolated from spinach leaves, and containing RUBISCO bound to the substrate RuBP have been grown and characterized. The crystals belong to the orthorhombic space group P2(1)2(1)2 with a = 173 A, b = 134 A and c = 112 A, and contain two enzyme complex molecules in the unit cell. Diffraction data to 2.5 A resolution have been collected on the sychrotron source at the photon factory in Japan. Initial structure determination has been carried out using the molecular replacement method. The RUBISCO molecule in the complex has the normal L8S8 subunit configuration, and difference electron density is clearly observed for the other component enzymes and the RuBP substrate.