Using field-theoretic methods, we obtain the low-density expansion of the free energy of systems where two ionic species with different valences (defined as the absolute value of the charge in units ofe, hereq1andq2) and hard-core radii (d1andd2) are present. The resulting expression (calculated up to order 5/2 in the concentration) is exact, and allows one to treat, in a unified way, electrolytes (whereq1∼q2andd1∼d2) and charged macro-particles suspensions (as for instance colloidal suspensions, where the size and the charge asymmetry are very large and play a crucial role). ©2000 American Institute of Physics.