We describe a two-wavelength laser-diode interferometer that is insensitive to external disturbances such as fluctuations in the wavelength of the laser diode and mechanical vibrations of the optical components. In sinusoidal phase-modulating interferometry this insensitivity is easily obtained by controlling the injection current of the laser diode with a feedback control system. Using an equivalent wavelength of 152 limprovided by two single-frequency laser diodes, we can measure the distance, rotation angle, and surface profile measurements with great accuracy. © 1991 Optical Society of America.