A modification of the Ashby‐Jephcott laser interferometer is described, by which both interferometric and schlieren information from an unsteady gas flow can be recorded at rates up to 5 MHz. The laser interferometer schlieren system (LIS) facilitates interpretation of the fringes recorded by the Ashby‐Jephcott system by recording both fringe and density gradient information in time. Use of the LIS is described in measuring &rgr;(t) for the shock and subsequent expansion flow from an open ended shock tube in air.