An interesting, hitherto unreported phenomenon involving interactions between polymer-coated, oppositely charged colloids is investigated experimentally and theoretically. Experimental stability for heteroaggregation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) coated, oppositely charged polystyrene spheres is quantified as a function of monovalent salt concentration by dynamic light scattering and compared with a primitive extension of DLVO theory, where the average volume fraction of polymer in the adlayers is used as the adjustable parameter. The energy barrier to aggregation is predicted to increase with increasing electrolyte concentration, behavior exactly opposite that of an electrostatically stabilized colloid. Two regions of heterostability may be defined: (1) at low ionic strength, stability ratios are less than unity and independent of triblock molecular weight, and (2) at moderate to high ionic strength, stability ratios exceed unity and depend on the triblock molecular weight. A critical salt concentration delineating these two regions may be identified, below which aggregation is more rapid than diffusion alone would allow and above which the heterodispersion becomes increasingly stable, reaching full stability for high molecular weight triblock adlayers.