An interferometric optical heterodyne technique has been developed especially for vibrational amplitude and phase measurements on auditory organs of live animals. Laser light diffusely scattered from the vibrating structure is used for the measurement. Continuous calibration and feedback compensation systems were developed to cope with the problems of drift in interferometer alignment and small background movements. Vibrational amplitudes from below 0.1 Å to above 400 Å have been detected on the posterior tympanic membranes of live crickets.Subject Classification: [43]65.20; [43]40.60; [43]35.65.