  Context. The IUE database provides a large number of UV high and
low-resolution spectra of RS CVn-type stars from 1978 to 1996. In particular,
many of these stars were monitored continuously during several seasons by IUE.
Aims. Our main purpose is to study the short and long-term chromospheric
activity of the RS CVn systems most observed by IUE: HD 22468 (V711 Tau, HR
1099, K1IV+G5V), HD 21242 (UX Ari, K0IV+G5V) and HD 224085 (II Peg, K2IV).
Methods. We first obtain the Mount Wilson index S from the IUE high and
low-resolution spectra. Secondly, we analyse with the Lomb-Scargle periodogram
the mean annual index S and the amplitude of its rotational modulation.
Results. For HD 22468 (V711 Tau, HR 1099), we found a possible chromospheric
cycle with a period of 18 years and a shorter cycle with a period of 3 years,
which could be associated to a chromospheric "flip-flop" cycle. The data of HD
224085 (II Peg) also suggest a chromospheric cycle of 21 years and a flip-flop
cycle of 9 years. Finally, we obtained a possible chromospheric cycle of 7
years for HD 21242 (UX Ari).
