Abstract. For developing a novel electron density and -temperature diagnostics based on fast He beam emission spectroscopy, experiments have been performed at the ASDEX Upgrade tokamak (AUG) in Garching and the JET tokamak in Culham. The measured He I emission profiles were compared with model calculations which are based on a collisional-radiative model developed by the ADAS group. For exploratory measurements at AUG one of the heating beam sources has been operated with pure helium. The beam emission profiles show satisfactory agreement with the profiles modelled using density and temperature profiles from other diagnostics. At JET and recently at AUG a small amount of helium was added to one standard deuterium ion source in order to produce a ``doped'' helium/deuterium beam. The respective measurements were performed using groups of identical pulses. In total, 11 different He I lines were investigated at JET with respect to their dependence on plasma density and -temperature. Seven lines were found to have sufficient intensity but the beam emission profile suffers from limited bandwidth of the spectrometer used. Good beam emission profiles could be obtained from recent AUG measurements showing a scatter of 9%.