In this article, we investigate the effects of magnetic field and porous medium on some unidirectional flows of a second grade fluid. These magnetohydrodynamic (MHD) flows are produced by the application of periodic pressure gradient or by the impulsive motion of one or two boundaries or by an oscillating plate. Modified Darcy's law has been used for the flow modeling. Seven illustrative examples have been taken into account and exact analytic solutions for velocity are obtained. Besides that analytic expressions for frictional forces have been established. The corresponding results of velocity and frictional forces in the absence of a porous medium and applied magnetic field Rajagopal, 1982; Hayat et al., 2000, can be obtained from the present analysis by taking M → 0 and K → 0. The similar results for a Newtonian fluid can also be gotten as a limiting case.