  We have observed CW lasing without inversion in a gas of hot rubidium atoms
in an optical cavity under conditions of electromagnetically-induced
transparency (EIT). The medium is pumped coherently and resonantly by a single
``coupling'' beam which also produces EIT in the lasing transition. The
steady-state intensity exhibits thresholds as a function of the atomic density
and the strength of the coupling beam. A theoretical model for an effective
three-level lambda system indicates that gain without inversion is possible in
this system if the two ground states are coupled by depolarizing collisions,
and if the decay branching ratios meet certain conditions.
