A new method of passive frequency stabilization is used to lock the laser output frequency to an atomic transition. A Michelson interferometer replaces the output coupler of a broadband standing wave dye laser. A sodium vapor absorber placed in one leg of the interferometer increases feedback only at the absorption frequency, forcing the laser to operate at this frequency. A fully Doppler-broadened vapor Results in simultaneous laser output at the 2S1/2-2P1/2 2S1/2-2P3/2 transition frequencies (dV=52 GHz) with linewidtns of 3 GHz each. An atomic beam of 1 MHz Doppler width produces simultaneous operation on both the [equation] transition frequencies (AV = 1.77 GHz) with linewidths of 1 MHz each. This technique should be applicable to other absorbers and may be of interest in optical pumping applications.