Towards an effective-lagrangian approach to fermion-loop corrections

We present a study of the non-local lagrangian approach to incorporate higher-order effects in e+e- -> n fermions. In its minimal version, the non-local lagrangian approach is found to exhibit problems with unitarity and high-energy behaviour. We identify the origin of these problems and obtain some first clues about possible solutions by investigating the zero-mode solutions of the Ward Identities. A numerical analysis of the importance of the zero-mode solutions is presented for four-fermion production processes.