From e.m.f. measurements on the concentration cells AgAgClRbCl (m)parallel to RbCl (m(f))AgClAg and Rb-amalgamRbCl (m(f))parallel to RbCl (m)Rb-amalgam, the ion and solvent transference numbers have been determined for aqueous RbCl solutions at molalities up to 7 mol kg(-1) over the temperature range from 25 to 55 degrees C. From the ionic transference numbers found, aqueous RbCl emerges as the most closely equitransferent salt bridge ever characterized. Considering also its high solubility (7.8 mol kg(-1) at 25 degrees C), RbCl is recommended as a built-in salt bridge for reference electrodes, in view of replacing the insufficiently equitransferent KCl bridges so far adopted by manufacturers.