Using bicrystal specimens of tin, the melting behavior of grain boundaries has been examined as a function of stress, heating rate, boundary angle, and impurity concentration. For small-angle boundaries (less than 12°) there is no tendency for the crystals to part at the boundary during melting. However, specimens with large-angle boundaries were consistently observed to separate at the boundary during melting. The temperature at which the separation took place, over a wide range of stress and heating rates, was the same as the melting temperature of the bulk material within the experimental accuracy of 0.02°C. The actual separation occurred a finite interval of time after the onset of general melting, and this interval was determined as a function of test conditions. Adding impurities to the material affected the melting temperature of the boundary in a manner conforming with that expected from their phase diagrams. Similar tests have been conducted on aluminum bicrystals. It has been determined (within an experimental accuracy of 0.25°C) that, as in the case of tin, the large-angle boundaries separated only after the melting temperature of the bulk material had been reached. Specimens of aluminum with low-angle boundaries (less than 14°) were not observed to separate at the boundary.