The experimental determination of the diffusion coefficient of given species into liquid alloys is difficult because of the unavoidable contribution of the convection. This remark applies to the case of tungsten (W) and carbon (C), introduced in liquid cobalt (Co) through the dissolution of tungsten carbide (WC). In the present work, the flow patterns produced by two different conditions of electromagnetic stirring of the liquid Co bath are computed. The electromagnetic forces which are induced by a high frequency induction coil are calculated with an integral method. They are introduced into a finite volume code for calculating the flow field. The velocity characteristics which are determined together with the experimental values of the rate constants [O. Lavergne, C, Allibert, Dissolution mechanism of WC in Co based liquids, High Temperatures, High Pressures 31 (1999)] for the dissolution of WC in the stirred liquid Co at 1450 degrees C lead to evaluate the diffusion coefficient to 2 10(-9) m(2) s(-1). It is remarkable that the values of D which are deduced for each case differ only from 14%.