In this paper we deal with the problem of free convection heat and mass transfer of a non-Newtonian power law fluid with yield stress from a vertical flat plate embedded in a fluid-saturated Darcy porous medium, considering Soret and Dufour effects. Here, we consider two different types of boundary conditions. In the first case, we assume the vertical wall is maintained at uniform wall temperature and concentration, and in the second case, we assume the wall is maintained at uniform wall heat and mass flux conditions. In both these cases, similarity solutions are possible. The results are analyzed with reference to the Soret and Dufour parameters along with other parameters that arise due to the non-Newtonian character of the fluid. Temperature and concentration profiles in the boundary layer are presented, together with the Nusselt and Sherwood numbers, for various combinations of problem parameters. Copyright © 2009 Begell House, Inc.