Staphylokinase, a 17 kDa protein, produced by certain strains of Staphylococcus aureus functions as a fibrin-specific plasminogen activator. During its interaction with plasminogen, staphylokinase is converted into a low molecular weight form by loss of ten amino-terminal residues. This low molecular weight form of recombinant staphylokinase has been crystallized using the hanging-drop vapor-diffusion technique with polyethylene glycol 4000 as precipitant. Crystals belong to the orthorhombic space group C222(1) with unit-cell dimensions a = 43.78, b = 59.86 and c = 103.25 A and one molecule in the asymmetric unit. These crystals diffract to about 2.4 A resolution.