abstract: We describe recent analytical and numerical studies of viscous and inviscid instability/bifurcation of slow (i.e., intermediate family) Lax-type MHD shocks in a duct, with standard polytropic equation of state. Our results indicate that planar slow shocks are typically unstable, the actual form of propagation in these modes being a nonplanar ``corrugated'' wave moving with the same speed. This study is one of the first numerical studies carried out for multi-dimensional viscous stability, a task that has only recently become possible, and which involves a number of difficulties not present in the one-dimensional case.