The response of a conducting fluid containing an embedded magnetic field (with &bgr;<1) to the sudden injection of material along the field lines is investigating using results from wave theory and numerical simulations of the nonlinear magnetohydrodynamic equations. A primary interest is the possible generation of, and the role played by, slow shocks in the medium response to the ejecta. We show that slow shock preceding an impermeable ejecta, the slow shock configuration deduced in the present computations is concave toward the ejecta ''driver.'' Fast-mode waves, which have not steepened into shocks, precede the slow shock and significantly alter the ambient medium (provided &bgr; is not too low). The slow waves are shown to play an important role in accommodating the driven ejecta. At low &bgr; the fast mode becomes primarily a transverse wave for parallel propagation, whereas the slow wave approaches a longitudinal, or sound, wave. The compressive effects of the motion then are principally transmitted by the slow shock, while the fast wave primarily just reorients the magnetic field. ¿ American Geophysical Union 1989