Precision measurements, extra generations and heavy neutrino

The existence of extra chiral generations with all fermions heavier than MZ is strongly disfavored by the precision electroweak data, The exclusion of one additional generation of heavy fermions in SUSY extension of Standard Model is less forbidden if chargino and neutralino have low degenerate masses with Deltam similar or equal to 1 GeV. However the data are fitted nicely even by a few extra generations, if one allows neutral leptons to have masses close to 50 GeV. Such heavy neutrino can be searched in the reaction e(+)e(-) --> N (N) over bar gamma at LEP-200 with total final luminosity of 2600pb(-1).