Multi-frequency signals were transmitted using a plane-wave transducer, through a water immersed phantom consisting of two finger cots, one containing 50% isopropanol alcohol and the other containing normal saline. The scattered ultrasound was received with a small hydrophone and detected with a quadrature detection system. The resulting phase quadrature data were submitted to a reconstruction algorithm which utilized the Rytov approximation to the Helmholtz equation in order to obtain the inverse solution for the distribution of refraction index within the phantom. In one experiment pseudo-random noise was generated by loading a 256 by 8-bit memory with random numbers and then synchronously reading these values through a D/A converter into an EMI power amplifier which drove the plane-wave transducer. The data received from each of 60 angles of view were spectral analyzed and specific frequencies selected for the cw reconstruction algorithm. Multiple frequency reconstructions will be shown as will the effect of frequency on the various underlying assumptions for the approximation. [Supported in part by Grants CA 24085 and NCI and ECS 7296008 from NSF.]