Mass is the most fundamental parameter in tracing a star’s evolution, Measured masses are provided by eclipsing binaries as summarized by Anderson (1991) and Torres et al. (2010). For O, B, and A stars a large fraction of the luminosity is emitted in the ultraviolet wavelength region, For this reason, temperatures determined incorporating these wavelengths are valuable. In this study we are using International Ultraviolet Explorer (IUE) spectra of eclipsing binaries with hot primaries to improve the mass–temperature relation. We provide an introduction to this project, including comparisons with model atmospheres. One way this will be used is in inferring a mass for the hot companions of Cepheids with known orbits.