The combined free convection dynamic boundary layer and thermal radiation boundary layer along a semi-infinite vertical porous plate with mass transfer has been analyzed. The chemical reaction for a very simple model of a binary reaction with Arrhenius activation energy is incorporated into the analysis. The fluid is considered to be gray, absorbing-emitting. Under such conditions, the coupled and unsteady non-linear momentum, energy and concentration equations of the combined layers are then made similar by introducing a time dependent length scale and by the usual method of similarity transformation. The similarity equations are then solved numerically by the method of superposition. The resulting velocity and t emperature distributions are shown graphically for different values of the parameters entering into the problem. The numerical values of the skin friction coefficient ( w ) and the Nusselt number (Nu ) are calculated and presented in a tabular form.