We present measurements by the Mark II experiment of the ratios of the leptonic partial widths of the Z boson to the hadronic partial width. The results are ee/had=0.037-0.012+0.016, &=0.053-0.0150.020, and /had=0.066-0.017+0.021, in good agreement with the standard-model prediction of 0.048. From the average leptonic width result, ll/had=0.053-0.009+0.010, we derive had=1.56-0.24+0.28 GeV. We find for the vector coupling constants of the tau and muon v2=0.310.31-0.30+0.43 and v2=0.050.30-0.23+0.34. © 1989 The American Physical Society.