  High-precision radial-velocity techniques, which enabled the detection of
extrasolar planets are now sensitive to relativistic effects in the data of
spectroscopic binary stars (SBs). We show how these effects can be used to
derive the absolute masses of the components of eclipsing single-lined SBs and
double-lined SBs from Doppler measurements alone. High-precision stellar
spectroscopy can thus substantially increase the number of measured stellar
masses, thereby improving the mass-radius and mass-luminosity calibrations.
