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 2 G. The relatively low strength of the magnetic field is explained by the large height of this stellar prominence ( \geq 0.67 stellar radii above the surface ) .