The T Tauri stars (TTS) are low mass pre-main-sequence stars
which show an enhanced continuum and line emission when
compared with main sequence stars of similar spectral types.
This excess is especially noticeable at ultraviolet wavelengths
where a major fraction of the gravitational binding energy
released during the accretion of the circumstellar material
is radiated and the stellar continuum emission fades dramatically.
The chrosmosphere and transition region also contribute significantly
to the UV spectrum. Disantangling both contributions and
understanding whether and how they may be related is a major
problem in star formation and early stellar evolution. We have
approached it by studying in detail, the overall UV properties
of the TTS and their variability.
Some classical TTS exhibit periodic UBVRI photometric variability with periods between 2 and 15 days. In some sources this variation is produced by the presence of hot spots on the stellar surface and reults from the modulation of the observed flux by rotation. The hot spots are likely to indicate the location of accretion shocks on the stellar surface. In this contribution we present a complete compilation of all the data on TTS available in the IUE (International Ultraviolet Explorer) Archive on this subject. There are 14 TTS (with hot and cool spots) that have been monitored in low dispersion with IUE: V410 Tau, BP Tau, RY Tau, HD 283572, T Tau, DF Tau, UX Tau, DN Tau, DR Tau, SU Aur, GW Ori, AB Dor, TW Hya and DI Cep. A detailed analysis of the light curves (UV continuum and main resonance lines) of these stars is presented.