Experiments on natural convection mass transfer adjacent to upward-facing inclined plates were performed by employing an electrochemical technique. For this purpose copper electrodes and an aqueous solution of cupric sulfate and sulphuric acid were used under limiting currents. Experiments showed that the Rayleigh number marking the onset of secondary flow in the form of vortex rolls in the primary natural convection varies markedly with the angle of inclination, decreasing with increasing departures from vertical, and that the vortex wavelength is almost independent of the surface inclination.