Abstract
Since its discovery as a variable star, 88 Her has undergone three photometric long-term variation cycles with transitions between Be-Shell and normal B phases. From the spectroscopic analysis of fifteen high resolution spectra obtained by the IUE satellite between 1981 and 1992, we were able to set parameters such as optical depths and location of line forming regions. We also found that the periodic radial velocity variations of UV Fe II lines agree with the orbital period (86.7 days). The residual intensity variations of Fe II lines have a cycle of 1560 days.An analysis of Mg II lines allowed us to measure for the first time the radial velocities of both stars of the binary system. Our aim is to ralate the properties of a circumstellar envelope to the variability phenomena observed in Be stars, in order to understand the mechanisms which cause them.