A new apparatus has been built for measuring solubility of solutes in supercritical fluids by direct injection of saturated supercritical-fluid solutions into a high-performance liquid chromatograph. To test the system, we measured the solubility of solid naphthalene in supercritical carbon dioxide at 55-degrees-C for pressures between 6.58 and 10.23 MPa. The system was designed to operate at pressures and temperatures up to 34 MPa and 140-degrees-C.