  Based on the IUE SWP spectra obtained between 1978 and 1994, the variations
of the UV continuum and the Ly-alpha and C IV emission lines of the broad-line
radio galaxy 3C390.3 are studied. The UV continuum between 1220 and 1990 A has
varied considerably. In 1991 August, the flux at 1360 A reached a maximum level
~27 times as high as its minimum level. At 1850 A, the continuum varies by a
factor of ~12. Significant variations are frequently observed in periods as
short as one month. The total flux of Ly-alpha and C IV emission varies by a
factor of ~5. Their profiles are fitted with one narrow component, unresolved
at the instrumental resolution of FWHM ~2000 km/s, and three broad components
(FWHM ~6000 km/s). The narrow component varies by a factor of ~2.5. The broad
components on the blue and red wings of the Ly-alpha and C IV emission profile,
which correspond to the double humps in the H-alpha and H-beta emission
feature, display a close correlation to the varying continuum, with a time lag
of ~45 days. The blue Ly-alpha component has been stronger than the red
component except for several epochs in 1980 and 1991. The C IV/Ly-alpha flux
ratio is ~0.4 for the narrow component. For the broad components, this ratio
varies considerably around an average value of unity. In 1991 March, the blue
Ly-alpha component was stronger than the red, while for C IV the red component
was stronger. Such differential variations do not match the accretion disk
characteristics. The findings suggest that the narrow- and broad-line region in
3C 390.3 may be associated with a radio jet.
