In this study, we numerically investigate the steady laminar natural convective flow and heat transfer of micropolar fluids in enclosures with a centrally located discrete heater in one of its sidewalls by applying a finite difference method. The other sidewall is kept at isothermal conditions, while horizontal walls are assumed to be insulated. Computations are carried out to investigate effects of the dimensionless heater length, the material parameter of the micropolar fluid, the Rayleigh number and the Prandtl number both for weak and strong concentration cases. Local results are presented in the form of streamline and isotherm plots as well as the variation of the local Nusselt number through the discrete heater. It was shown that micropolar fluids presented lower heat transfer values than those of the Newtonian fluids. An increase at the material parameter, K is shown to decrease the heat transfer. The results for K = 0, which corresponds to the Newtonian fluid case is compared with those available in the existing literature and, an excellent agreement is obtained. (c) 2005 Elsevier Ltd. All rights reserved.