Field emission from carbon nanotubes has been measured. Typical values are 100-1000 nA at a nanotube bias of $-$80V. The amount of field emission is found to depend strongly on the state of the nanotube tip. This should serve in future work as a good indicator of tip condition. It is believed that open tip nanotubes unravel at their ends while field emitting to form a carbon chain. An atomic chain being the ultimate geometry for a field emitter, nanotube tips may have applications for monoenergetic electron sources, electron microscope field emitters, and electron holography.