Turbulent mixed convection adjacent to an isothermal vertical flat surface is analyzed for the buoyancy assisting flow situation. Results are presented for air (Pr=0.7) flowing at various velocities and for a range of plate-free stream temperature differences. Closure of the governing, time averaged, turbulent equations for the mean flow quantities is attained by using a modified K-ε model which accounts for the influence of buoyancy induced forces on the turbulent quantities. The set of governing equations is solved by an implicit marching scheme similar to the one used by Patankar and Spalding. The results demonstrate clearly that the presense of small free stream velocities has the effect of delaying the transition from laminar to turbulent flow, thus creating a region where the predicted mixed convection heat flux is smaller than the equivalent turbulent natural convection. The numerical results are in qualitative agreement with available experimental measurements.