An S-Matrix ansatz is used to determine the mass and width of the Z boson,
as well as the contributions of gamma/Z interference and Z boson exchange t
o fermion-pair production. For this purpose we use hadron and lepton-pair p
roduction cross sections and lepton forward-backward asymmetries that have
been measured with the L3 detector at centre-of-mass energies between 87 Ge
V and 189 GeV. (C) 2000 Elsevier Science B.V. All rights reserved.