Demixing pressures for solutions of isotactic polypropylene (M-w=216 000; M-w/M-n=7.2) in n-pentane have been determined for polymer concentrations of 1, 3, 5, 10, 15 and 30 mass% in the temperature range from about 410 to 480 K. Isotactic polypropylene is completely miscible in n-pentane at these concentrations at pressures above about 10 MPa. Limited data are also presented for miscibility in binary mixtures of n-pentane+carbon dioxide. In the presence of carbon dioxide, higher pressures are required for complete miscibility.