We report the results of particle growth in a polydisperse blend system as a function of(i) heat treatment temperature (190, 220, 250, and 280 degrees C) and (ii) time of heat treatment (0-290 min) for three blends of isotactic polypropylene and linear low-density polyethylene, prepared by melt extrusion. To a first approximation, the growth of the particles obeys the t(1/3) law; however, the polydispersity of the solute polymer has an effect on this relationship. The dependence on molecular weight is analyzed, and it is shown that for polydisperse solute the gradient of growth should decrease with time.