Time-resolved multiangle light scattering is used to measure absolute heteroaggregation (heterocoagulation) rate constants in aqueous binary colloidal particle mixtures. These measurements are possible despite the simultaneous occurrence of homoaggregation (homocoagulation). The procedure can be used with static as well as with dynamic light scattering, even though the latter technique is more accurate and more sensitive. The approach exploits the differences in the form factors of the asymmetric particles dimers. Particles of unequal size are therefore needed, but the method is sensitive already to 10% difference in size. We have applied the technique for latex particles in 100-200 nm size range, where the Rayleigh-Gans-Debye approximation is accurate, and obtained the formation aggregation (coagulation) rate constants for the asymmetric dimers as a function of the ionic strength up to 300 mM.