Extra generations and discrepancies of electroweak precision data

It is shown that additional chiral generations are not excluded by the latest electroweak precision data if one assumes that there is no mixing with the known three generations. In the case of heavy extra generations, when all four new particles are heavier than Z boson, quality of the fit for the one new generation is as good as for zero new generations (Standard Model). In the case of neutral leptons with masses around 50 GeV (partially heavy extra generations) the minimum of chi(2) is between one and two extra generations. (C) 2002 Elsevier Science B.V. All rights reserved.