  We present synthetic ultraviolet spectra of metal-poor star-forming galaxies
which were calculated with the Starburst99 package. A new spectral library was
generated from HST observations of O stars in the Large and Small Magellanic
Clouds. The corresponding mean metallicity of the synthetic spectra is
approximately 1/4\Zs. The spectra have a resolution of 1\AA and cover the
spectral range 1200-1600\AA. A set of model spectra was calculated for a
standard initial mass function and star-formation history and is compared to
synthetic spectra at solar metallicity. We find that the spectral lines are
generally weaker at lower metallicity, as expected from the lower elemental
abundances. Stellar-wind lines, however, show a more complex behavior: the
metallicity dependence of the ionization balance can be important in trace
ions, like N$^{4+}$ and Si$^{3+}$. Therefore the strength of \nv and \siiv does
not scale monotonically with metallicity. We compare our new models to
ultraviolet spectra of NGC 5253 and \cB, two star-forming galaxies with 1/4
solar metallicity at low and high redshift, respectively. The new library
provides significantly better fits to the observations than earlier models
using the \Zs library. We discuss the potential of utilizing stellar
photospheric and wind lines to estimate the chemical composition of
star-forming galaxies. The new metal-poor synthetic spectra are available via
the Starburst99 website.
