The data obtained by the vertical seismic profiling (VSP) method require unique processing before interpretation. An important step is the separation of upgoing and downgoing signals by application of an f-k velocity filter and muting of the direct wave. Similarly, if the VSP section is transformed to the p-tau plane, the upgoing and downgoing wave fields become separable because they map to different p-tau quadrants according to their dips. This allows either wave field to be reconstructed by application of the inverse Radon transform after windowing in the p-tau plane.Results obtained by the Radon transform wave field separation (RTWS) method are similar to those obtained by f-k velocity filtering. However, by implementing an amplitude-ratio testing filter in the forward slant stack, the quality of the reconstructed wave field is much improved. For a specific range of p-stack values in the forward transform, this filter sorts and removes the unwanted events from the desired ones by testing their consistency in stack amplitudes.Synthetic examples of separating the upgoing wave field from a full VSP wave field by both methods are presented.