  We present the analysis of six nights of spectroscopic monitoring of two
young and fast rotating late-type stars, namely the dMe star HK Aqr and the
dG/dK star PZ Tel. On both stars we detect absorption features reminiscent of
signatures of co-rotating cool clouds or prominences visible in H$\alpha$.
Several prominences on HK Aqr show periodic variability in the prominence
tracks which follow a sinusoidal motion (indication of prominence
oscillations). On PZ Tel we could not find any periodic variability in the
prominence tracks. By fitting sinusoidal functions to the prominence tracks we
derive amplitudes and periods which are similar to those of large amplitude
oscillations seen in solar prominences. In one specific event we also derive a
periodic variation of the prominence track in the H$\beta$ spectral line which
shows an anti-phase variation with the one derived for the H$\alpha$ spectral
line. Using these parameters and estimated mass density of a prominence on HK
Aqr we derive a minimum magnetic field strength of $\sim$2G. The relatively low
strength of the magnetic field is explained by the large height of this stellar
prominence ($\ge$ 0.67 stellar radii above the surface).
