Natural convection flow and heat transfer of a viscous fluid confined between two vertical parallel plates is analytically investigated taking volumetric heat generation into account. It is assumed that one of the plates is flat and the other has periodic protrusions. The short protrusions are assumed to be periodic in span, facilitating a mathematical representation for the arbitrary shape protrusion by a Fourier series. The governing equations of momentum, and energy are solved by regular perturbation method. The flow, and heat transfer characteristics are determined for different values of Grashof number, wall temperature ratio, heat source parameters, protrusion frequency and spacing. © 1995 Kluwer Academic Publishers.