A method is presented for acoustic passive multipath target tracking in the ocean. The method accounts for the inhomogenuity of the medium by integration of a prefilter into the tracking algorithm. The prefilter uses the output of an eigenray acoustic model computed over a two dimensional (2-D) grid of possible target positions (depth,range). The function is inverted and interpolated to form a transfer function from propagation time delay differences to range and depth. A three dimensional (3-D) maneuvering target estimator is used and its performance is evaluated. The results demonstrate the strong effects of the medium on the tracking concept.