The problem of transient, laminar, three-dimensional natural convection flow over an inclined permeable surface in the presence of a magnetic field and heat generation or absorption effects is considered. The order of the governing differential equations for this investigation is reduced by using transient non-similar transformations. The resulting initial-value problem is solved numerically by an accurate, implicit, finite-difference line by line marching scheme. A parametric study is performed to illustrate the influence of the Prandtl number, Hartmann number, heat generation or absorption coefficient, and the surface suction or injection parameter on the velocity and temperature fields as well as the transient development of the skin-friction coefficients and the Nusselt number. These results are displayed graphically to show special aspects of this flow and heat transfer situation. (C) 2000 Elsevier Science S.A. All rights reserved.