  The characteristics of black-hole X-ray binaries can be used to obtain
information about their evolutionary history and the process of black-hole
formation. In this paper I focus on systems with donor masses lower than the
inferred black-hole masses. Current models for the evolution of hydrogen-rich,
massive stars and of helium stars losing mass in a wind cannot explain the
current sample of black-hole mass measurements. Assuming that the radial
evolution of mass-losing massive stars is at least qualitatively accurate, I
show that the properties of the BH companions lead to constraints on the masses
of black-hole progenitors (at most twice the black-hole mass) and on the
strength of winds in helium stars (fractional amount of mass lost smaller than
about 50%). Constraints on common-envelope evolution are also derived.
