Unsupported films of nitrocellulose of 0.25 micron and less in thickness bonded immediately and spontaneously in air to solid surfaces which they were made to touch. Bond strength increased with diminishing film thickness. Similar behavior was shown by films of gold, regenerated cellulose, polymethyl methacrylate, and gelatin. This bonding power of nitrocellulose films, which was apparently not attributable to static electricity or to mechanical joint formation, was lost while immersed in water, benzene, or hexane, but was regained upon removal and drying.