This paper discusses the performance of a digital matched filter receiver matched to a biphase-modulated signal in a clutter environment consisting of other biphase-modulated signals. Analytic results for a white-Gaussian model and for a non-linear capture model are compared with simulation results obtained from an IBM 7094 computer. The white-Gaussian model is in general agreement with the simulation results for equal power clutter signals; the capture model and the simulator yield similar results when a dominant clutter source is present.