Based on 520 000 fermion pairs accumulated during the first three years of data collection by the ALEPH detector at LEP, updated values of the resonance parameters of the Z are determined to be M Z =(91.187±0.009) GeV, Γ Z =(2.501±0.012) GeV, σ{had/0}=(41.60±0.27) nb, and R l=20.78±0.13. The corresponding number of light neutrino species is N ν=2.97±0.05. The forward-backward asymmetry in lepton-pair decays is used to determine the ratio of vector to axial-vector couplings of leptons: g {/V 2}( M {/Z 2})/ g {/A 2}( M {/Z 2})=0.0052±0.0016. Combining this with ALEPH measurements of the b and c quark asymmetries and τ polarization gives sin2θ{/W eff}=0.2326±0.0013. Assuming the minimal Standard Model, and including measurements of M W / M Z from p bar p colliders and neutrino-nucleon scattering, the mass of the top quark isM_{top} = 156 ± begin{array}{*{20}c} {22} \ {25} \ ± begin{array}{*{20}c} {17} \ {22Higgs} \ GeV.
