The long-time regime coarsening in a phase-segregated blend of hydrogenated polybutadiene (HPB) with high-density polyethylene (HDPE) was studied. The blend consisted of 10 wt % of HPB in a HDPE matrix. The morphology of the system was studied by etching the HPB particles from the HDPE matrix and observing the etched specimens in a scanning electron microscope. The average volume of the HPB particles was found to increase with storage time in the melt, and to follow a temporal exponent of 1 in agreement with the predictions of the Ostwald ripening theory. This indicated that the particles coarsen by the evaporation-condensation mechanism on which the Ostwald ripening theory is based. The rate constant from the Ostwald ripening theory was calculated and compared to the rate constant determined from the experimental data. The theoretical rate constant, K, calculated from Ostwald ripening theory, was 3.6 X 10(-18) cm(3)/s compared to an experimentally determined rate constant of 4.8 X 10(-18) cm(3)/s. The agreement between the theoretical and experimental rate constants was quite good. The significance attached to the good agreement between the theoretical and experimental rate constants might be mollified to some extent by the uncertainty involved in the parameters used to calculate the theoretical rate constant; viz. the interfacial tension, mutual-diffusion coefficient, and equilibrium concentration of the HPB in the matrix phase that are not known to high accuracy. In reality, because other theories were used to determine the interfacial tension, mutual-diffusion coefficient, and equilibrium phase compositions, this study was a test of several theories simultaneously. However, the agreement of the experimental temporal exponent and rate constant with the predictions of Ostwald ripening theory strongly indicates that the HPB/HDPE system coarsens by the evaporation-condensation mechanism upon which the Ostwald ripening theory is based.