Conjugate convective-conductive heat transfer in a rectangular enclosure under the condition of mass transfer within cavity with local heat and contaminant Sources is numerically investigated. Mathematical model, describing a two-dimensional and laminar natural convection in a cavity with heat-conducting walls, is formulated in terms of the dimensionless stream function, vorticity, temperature and solute concentration. The main attention is paid to the effects of Grashof number (Gr), Buoyancy ratio (Br) and transient factor on flow modes, heat and mass transfer. (C) 2008 Elsevier Ltd. All rights reserved.