This paper presents an analytical solution for the dispersion of a solute in an electrically conducting fluid flowing between parallel plates with a transverse magnetic field and uniform wall suction. For fixed values of the suction parameter P and Schmidt number Sc, the longitudinal diffusion coefficient K decreases rapidly with increase in the magnetic parameter M. Further, for fixed Mand Sc, it is found that K increases with increasing P. The effect of variation of Sc on K is found to be very small.