Analysis of simultaneous magnetic field and plasma data by Pioneer 7 reveals the existence of a well-defined bow shock structure at geocentric distances of 350--440 RE. Bow shock physical parameters are computed by an iterative least squares technique applied to combined plasma and magnetic field data. Observed features suggest that at those distances from the earth the bow wave still preserves its near-earth characteristics. In particular, the normal ? to the shock surface is in agreement with the predicted ~20¿ Mach angle. Deviations from these typical conditions are interpreted in terms of a local distortion of the shock geometry.