A high-pressure cell for synchrotron small-angle X-ray scattering (SAXS) studies of protein solutions is described. The design was optimized for use at up to 400 MPa in liquid pressure and with 8−12 keV X-rays with particular emphasis on the ease of use. The high-pressure cell was fabricated from corrosion-resistant Inconel 725 (Special Metals Corporation, Huntington, WV, USA) and featured Poulter-type windows [Poulter (1932). Phys. Rev. 40 , 861–871]. Flat natural diamonds, 500 µm thick, were recycled from diamond anvil cells and were shown to perform well as high-pressure SAXS windows. For a simple and effective method of sample isolation, disposable plastic sample cells with a defined path length and reproducible parasitic scattering were designed. These sample cells enable efficient use of synchrotron time. The cells facilitate rapid and easy sample changes, eliminate the need to clean the cell between sample changes, and reduce the sample volume to as low as 12 µl. The disposable cells can also be used separately from the high-pressure cell for SAXS measurements at ambient pressure and temporary storage of samples. The performance of the apparatus is demonstrated with T4 lysozyme.