Falling film evaporators are being used increasingly in the chemical process industries for multicomponent mixtures. Experimental data for the heat transfer characteristics are lacking, especially for wide-boiling-range mixtures. This study obtained experimental measurements of heat and mass transfer for a binary mixture evaporating in downflow in a heated vertical tube. Local heat fluxes, wall temperatures, and bulk fluid temperatures were measured for ranges of film flow rate and fluid composition. Boiling ranges of up to 55 C were investigated, using several mixtures of ethylene glycol and water. The tests were run at atmospheric pressure, with heat fluxes ranging from 3000 to 25000 W/m/sup 2/, and film Reynolds numbers of 300 to 3000. The results show that the heat transfer coefficient for the mixtures is a weak function of wall superheat, tube length, and film Reynolds number, but a very strong function of mixture composition. A preliminary analysis indicates the presence of a significant mass transfer resistance, contrary to earlier speculations.