The UV spectrum of galaxies provide us with the unique chance to detect those hot stellar components, which normally do not appear in the visible spectrum. Such components, interpreted as possibly due to horizontal-branch stars, have been found in spectra of early-type galaxies. All these spectra exhibit an UV excess shortward of 3000 A with respect to the energy distribution of a K-type star. UV excess is present in different amount also in spectra of late-type galaxies, but the data are fragmentary.
There is hope to define a standard UV spectrum of nearby elliptical galaxies to compare with that observed in the visible region in distant galaxies. This would allow the determination of the evolutionary effect.
The emission lines in elliptical galaxies are found much stronger than one would expect if the physical conditions are similar to those of HII regions.
Direct images of galaxies allow to trace the spiral structure defined by hot stars and to study the UV luminosity profile in the nuclear region.