Recombinant proteins of monomeric and dimeric B-domain repeats of a Staphylococcus aureus FDA 574 collagen-binding adhesin have been crystallized. The single repeat unit (B1) was crystallized in a body-centered orthorhombic lattice with a = 96.9, b = 101.3, c = 120.8 Å in either the 1222 or 1212121 space group. These crystals diffracted to 2.5 Å resolution and the calculated V(m) values of 3.2 and 2.2 Å3 Da-1 suggest the possibility of a dimer or a trimer in the asymmetric unit. The two-repeat fragment (B1B2) crystallized in the orthorhombic space group P212121 with cell dimensions a = 42.4, b = 79.4, c = 130.4 Å and diffracted to 2.3 Å resolution. For this species, the calculated V(m) value of 2.2 Å3 Da-1 indicates the presence of a monomer in the asymmetric unit.