This paper concentrates on the analytical study of the effect of thermal dispersion on fully developed forced convection in a parallel-plate channel partly filled with a fluid saturated porous medium. The walls of the channel are subject to a constant heat flux. The central part of the channel is occupied by a homogeneous fluid, while peripheral parts of the channel are occupied by a fluid saturated porous medium of uniform porosity. It is assumed that the momentum flow in the porous region is described by the Brinkman-Forchheimer-extended Darcy equation. Since thermal dispersion becomes appreciable in high speed flows, that is, for the same situation when accounting for the Forchheimer term in the momentum equation is essential, the effect of thermal dispersion should be taken into account simultaneously with accounting for the Forchheimer term in the momentum equation. The objective of the present research is to determine in which situations accounting for thermal dispersion can significantly influence the solution.