  Several works have recently shown that there is an important extra
line-broadening (usually called $macroturbulence$) affecting the spectra of O
and B Supergiants that adds to stellar rotation. So far, the only (very recent)
physical explanation for the appearance of $macroturbulence$ relates to
oscillations. This is a plausible explanation, but no direct evidence
confirming its validity has been presented yet. We recently started an
observational project to obtain constraints on the time-scales of variability
associated to this extra line-broadening and its possible origin. Our
observational strategy consists of the study of a well selected group of O and
B stars, for which we obtain time series of high-quality spectra. We present
some preliminary results from our first campaign with<EMAIL_ADDRESS>