We discuss the determination of neutron star masses in X-ray binaries and explain the importance of such measurements. Examples are given of two of our recent neutron star mass determinations, in Cen X-3 and Vela X-1. We then discuss prospects for improving such measurements with SALT and the possibility of determining only the seventh neutron star mass in such a system by measuring the radial velocity curve of the recently discovered counterpart to the X-ray pulsar OAO1657--415
