  We present a direct measurement of the parity violation parameter Ab, derived
from the left-right forward-backward asymmetry of b quarks tagged via leptons
from semileptonic decays. The lepton identification algorithm combines
information from tracking, calorimetry and from the SLD Cherenkov Ring Imaging
Detector. The value of Ab is extracted using a maximum likelihood fit to the
differential cross section for fermion production. Vertexing information and
decay kinematics have been used to discriminate among the different sources of
tagged leptons. A new treatment of mixing effects and of background
contamination has been introduced and a new vertexing algorithm has been used
in the muon analysis. Based on the 1993-1998 SLD sample of 550K hadronic Z0
decays with highly polarized electron beams, we have measured Ab with a ~3%
statistical error.
