  We demonstrate room-temperature spin-polarized ultrafast ($\sim$10 ps) lasing
in a highly optically excited GaAs microcavity. This microcavity is embedded
with InGaAs multiple quantum wells in which the spin relaxation time is less
than 10 ps. The laser radiation remains highly circularly polarized even when
excited by nonresonant elliptically polarized light. The lasing energy is not
locked to the bare cavity resonance, and shifts $\sim$10 meV as a function of
the photoexcited density. Such spin-polarized lasing is attributed to a
spin-dependent stimulated process of correlated electron-hole pairs. These
pairs are formed near the Fermi edge in a high-density electron-hole plasma
coupled to the cavity light field.
