Effects of new leptons in electroweak precision data

We obtain limits on generic vectorlike leptons at the TeV scale from electroweak precision tests. These limits are complementary to the ones obtained from lepton flavor violating processes. In general, the quality of the global electroweak fit is comparable to the one for the standard model. In the case of an extra neutrino singlet mixing with the muon or electron, the global fit allows for a relatively large Higgs mass (${M}_{H}\ensuremath{\lesssim}260\text{ }\text{ }\mathrm{GeV}$ at 90% C.L.), thus relaxing the tension between the direct CERN LEP limit and the standard model fit.