  As part of an extensive multi-wavelength monitoring campaign, the
International Ultraviolet Explorer satellite was used to observe the broad-line
radio galaxy 3C 390.3 during the period 1994 December 31 to 1996 March 5.
Spectra were obtained every 6-10 days. The UV continuum varied by a factor of 7
through the campaign, while the broad emission-lines varied by factors of 2-5.
Unlike previously monitored Seyfert 1 galaxies, in which the X-ray continuum
generally varies with a larger amplitude than the UV, in 3C 390.3 the UV
continuum light-curve is similar in both amplitude and shape to the X-ray
light-curve observed by ROSAT. The UV broad emission-line variability lags that
of the UV continuum by 35-70 days for Ly-alpha and CIV 1549; values larger than
those found for Seyfert 1 galaxies of comparable UV luminosity. These lags are
also larger than those found for the Balmer lines in 3C 390.3 over the same
period. The red and blue wings of CIV and Ly-alpha vary in phase, suggesting
that radial motion does not dominate the kinematics of the UV line-emitting
gas. Comparison with archival data provides evidence for velocity-dependent
changes in the Ly-alpha and CIV line profiles, indicating evolution in the
detailed properties and/or distribution of the broad-line emitting gas.
