A new crystal form of the bovine oligomeric lens protein beta B2 has been grown in the presence of calcium acetate. The crystals are orthorhombic, I222 or I2(1)2(1)2(1), with cell dimensions a = 77.8 A, b = 83.6 A, c = 109.2 A. This new crystal form, which diffracts to at least 2.5 A, has a and b cell dimensions that are half those of the original crystal form, although there is no simple relationship between the c cell dimensions. The new crystal form reported here contains only one subunit per asymmetric unit, indicating that the dimer lies on a crystallographic 2-fold axis, and is a suitable candidate for molecular replacement studies.