The output amplitude and frequency of a conventional internal mirror He-Ne laser have been stabilized using a new approach. For this scheme, the polarization properties of three axial-mode spectra are examined. Differences in intensities between the side mode spectra are detected using a newly designed Michelson interferometer. The resultant differential signal is used to maintain the central mode spectrum at maximum gain. The cavity length of the laser is thermally controlled with a drift-compensated interferometer using differential photodetection feedback. The result is an intense and stabilized single-mode output laser. Excellent amplitude (+/-0.1%) and frequency (+/-2 parts in 10(9)) stability are achieved.