Atomic beams of In and A1 were ionized on a heated Ir surface in a good vacuum. Curves of ion current density versus reciprocal surface temperature are plotted with atomic reservoir temperature as parameter, yielding also desorption energies of 4 to 5 eV. Ion current densities from [inverted lazy s] 10−9to 10−6A/cm2were measured in the temperature range from [inverted lazy s] 1400 to above 2000°K. The calculated ionization efficiency for the system In on Ir is about 40% taking into account excited atomic states.