  We present the detection of a radio-emitting jet from the black-hole
candidate and X-ray binary source Cygnus X-1. Evidence of a bright core with a
slightly extended structure was found on milliarcsecond resolution observations
with the VLBA at 15.4 GHz. Later observations with the VLBA (and including the
phased up VLA) at 8.4 GHz show an extended jet-like feature extending to
approx. 15 mas from a core region, with an opening angle of < 2 degrees. In
addition, lower resolution MERLIN observations at 5 GHz show that the source
has < 10 per cent linear polarization. The source was in the low/hard X-ray
state during the observations, and the results confirm the existence of
persistent radio emission from an unresolved core and a variable relativistic
(> 0.6c) jet during this state.
