The authors formulate the natural thermosolutal convection in an elongated enclosure of horizontal axis, partitioned by a vertical porous layer. They use the Boussinesq approximation, the stream function, the vorticity and the extended Darcy-Brinkman formulation to describe the transfer occurring in the porous layer. The chosen dimensionless parameters allow obtaining a single set of conservation equations, valid both in the two fluid compartments and in the porous layer. They solve numerically the set of coupling equations using the volume control approach. After recovering some literature results, they study, in an enclosure of square section which is partitioned by a porous layer into two equal fluid compartments, the influences of the main parameters on the Nusselt and Sherwood numbers for the Rayleigh number varying from 10(4) to 10(7), the Darcy number from 10(-5) to 10(-3), the thermal conductivity ratio from 1 to 100, the solutal diffusivity ratio from 0.01 to 1, the Lewis number from 0.1 to 5 and the buoyancy ratio from -5 to 5. For Ra greater than or equal to 10(4), a multicellular convective fluid flow can appear when -3 less than or equal to N less than or equal to -0.5 and if, at least, Le, R-k or R-d is different from unity. (C) 2000 Elsevier Science Ltd. All rights reserved.